Erin, I bought an angel sounds doppler from ebay for about $35 - you use it with a bit of baby oil to conduct the sound, we heard babies heart beat from about 11 weeks and always find the heartbeat pretty easy, but thats just my experience.

I've found it reassuring as we have an IVF pregnancy and I worry alot, but I only use it about once a week as now I can feel bubs moving about. I did um and arr about buying it was was worried it wouldn't always pick up the heartbeat and I'd worry more, but for us this hasn't been an issue.

The angel sounds one also allows you to plug it into your PC microphone outlet and then you can record the heartbeat to send to family or friends etc, which is pretty cool

Its one of my best buys since pregnant

Hope this helps
Naomi