OMG $500 - no way!! I've never spent more than $100 (10-15 ppl) so you should well and truly be able to get away with doing a bigger group for $150 or so!!!

Here's what I do - make up a theme. I buy serviettes with pictures on them but then just get cheap coloured plastic plates (matching or contrasting colour) and cups from The warehouse or go lo or whatever.

Instead of buying licensed character stuff - I buy several sheets of stickers (on chosen theme) and stick them to cups, party hats etc

Hats - you can make these yourself using cardboard or just buy cheap plain party ones and decorate themyourself. One year I got the kids to make their own crowns - decorating them with stickers etc - they had a ball.

Games - think simple like treasure hunts, follow the leader, simon says, and funny races like trying to run with a balloon between your knees. Not every game needs a prize.

Lollybags - either use decorated cups wrapped in cellophane or you can jazz up your own paper bags. Don't go overboard with the take-home stuff. Kids get that much cr*p from parties etc it stops being special.

Decorations - I just do balloons and crepe paper streamers in the colours that match my theme. You can have a bit of crepe paper on the table if you want to add to the colour. Lots of balloons are great for a 1 yo party - just buy the helium-grade ones (big w sells them) so they burst on the grass and blow them up yourself with a balloon pump.

Kids that age really love bubbles. I suggest getting some of those cheap wedding bubble bottles for each of the kids. Never stops being fun.

Food - simple is best. I usually do 3-4 savory things, plus 3-4 sweet things (including fairy bread of course LOL) plus fruit. IN a park you could get away with appointing an uncle or someone to cook sausages in bread.

Just remember it's a party - the point is getting together and having FUN.