Bought my sonoline doppler on ebay for $40
They have them at motherhood maternity clothing store and babies r us, also at gift shops in some hospitals that you may deliver at but are a bit pricier there. I'd check out kids resale shops also, but may be a hit or miss with those!
Im trying to decide to. I found a site called fetaldoppler.net but haven't decided if im gunna get it or not.