I have purchased one of those prenatal heartbeat listening things from Kmart - for $40. But you can only use it from weeks 21... so I'm waiting, waiting, waiting....
But if it works (?) - you can record the heartbeats and load it onto your computer for emailing! You can also record your own heartbeat... and record that for baby when they are born.

There are more expensive dopplers available - quite a few on eBay... but you're usually looking around $100 upwards. You can use those ones from 12 weeks onwards.

You can also hire professional dopplers for around $40 a month. Just google "hire doppler" and a couple of sites should pop up.

One thing I noticed was a prenatal stethoscope was available on eBay - from the USA - and it was reasonably cheap (like around $25 - plus postage).