DH and I did the courthouse ceremony and we not only planned and pulled it off in under 6 weeks, but we only spent around $3000.
You can find the details on paperwork etc by googling it and finding your state's requirements, we're in QLD and all up the paperwork was around $300. You just file the 'Notice of Intention to Marry' bit with your local courthouse or whatever and that's about $275, then the marriage licence itself is another $65 or so dollars.
We just printed the Intent form, filled it out, lodged it at the courthouse and they asked us to pick a date there and then - we chose a date five weeks from that day (there's a minimum 'cooling off' period of around four weeks so we gave ourselves an extra week just to be sure we had time to put everything in place), and booked it in.
If you do it at the courthouse, they usually have special days when they perform marriages so don't worry, you won't be sitting in the lobby with a bunch of crims awaiting their turn in front of the judge!! Our court days up here are Mon, Thurs and Fri so Tues and Wed are the 'wedding' days.

You can wear whatever you want - be as formal or as casual as you like. The courthouse allows up to around 20 'guests', you can always ask if you want more people there because I'm sure they're happy to have people stand in the back (they go on how many seats they have in the particular room they use). DH and I didn't tell anybody except our parents we were getting married, our closest friends had no idea we were even engaged until we posted the wedding photos on MySpace!! So we had a total of seven guests - two parents and one sibling on each side, and my grandmother.
I bought a simple black cotton knee-length dress for $50 from a local boutique, as I was five and a half months' pregnant and wanted something I could wear again - I still wear it quite often now and it's lovely. I did my own makeup, and a friend of my mum's (who used to be a hairdresser but is now a SAHM and does friends' hair in her kitchen for a bit of pocket money) did my hair for $25. DH just wore a pair of black trousers that were his work uniform when he was in retail, a black button-down shirt, a tie that I picked up from an op shop for $1.50 (it fit with our 'colour scheme' of black, red and white) and his black Chuck Taylors. I had bought my shoes months before for a friend's 30's-themed birthday party and just wore them.

Our wedding bands cost us a little bit, DH just grabbed his out of the case and paid $140, mine was supposed to be the same price but because I wanted it in white gold and it had to be resized to fit my tiny fingers, it ended up being about $195. My engagement ring is a simple silver band with a CZ, it cost me $30 (and another $20 to get it resized).

After the 10-minute ceremony, we went around town to take some photos at some pretty locations (we have a lookout with a waterfall, and our Botanic Gardens have a lovely Japanese Teahouse and a pretty pond that looks nice in photos) and everybody just brought their own cameras to take pictures. Nothing professional, but you really don't need it unless your family are butt-senseless at taking photos - besides, you can do some amazing stuff with Photoshop and similar programs these days... It was good too because we had full control over what we wanted to do as far as posing etc, we're not the type to do all the cheesy wedding poses so all our shots are just beautiful, natural pics. Of course there were some shockers because only my dad is a professional photographer, but with six cameras aimed at us we managed to get a lot of good ones, and didn't cost us a cent bar taking the USB cards to Harvey Norman to get them printed!

We'd booked a night in a motel room to treat ourselves, get out of the house for the night, so after a quick trip home to get an overnight bag together we went to the motel and had dinner at the restaurant there. Everyone paid for their own meals and drinks (which was good because DH's parents are borderline alcos and DH's brother ordered an expensive seafood platter which he ended up eating maybe a quarter of!!), we'd ordered a slab mud cake from the Cheesecake Shop for around $75 including decorations, and that was our dessert.

We didn't have flowers, or a bridal party, or any of the trimmings that we just don't see as necessary to celebrate a marriage of two people who want to just belong to each other. It was a very fun, relaxed day with no hassles (apart from a couple of days before when my wedding ring still hadn't arrived at the jeweller's and there was a minor freakout about having it on time!! luckily it got sorted out), no *****fights, no pressure to make a big impression or impress people.. no jealousy about picking one friend over another to be in the bridal party, no extra expense of having to provide food etc for people I'm not particularly close to but felt obligated to invite (ie, we didn't invite anybody so nobody could feel left out!)... it was just DH and I, being joined together in front of our families and enjoying the day because it truly was all about US, not flowers, cakes, dresses, jewellery, or comparing our wedding to those of our friends.

I'd seriously recommend it to anybody who's on a budget or has hassles with certain friends and/or family who should be acting their age and know better than to cause trouble. Like I said, it was so much cheaper than these big weddings we see everywhere now, we didn't go into debt to put on a big show for everyone and at the end of the day, it really was just all about being married and being in love and declaring that in front of our families.

I hope that info gives you something to work with, or answers some questions you have about the whole process... if you need anything else just PM me, I'm happy to help out!