Here is a link to the one I bought off ebay http://cgi.ebay.com/NEW-2009-3MHZ-FETAL-DOPPLER-BABY-HEART-MONITOR-BIG-LCDd_W0QQitemZ200328013903QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2ea47ae84f
I heard the heartbeat from 8 weeks! It's been absolutely fantastic for both my pregnancies.
Since you are further along maybe you should think about getting an angelsounds one? They are very cheap and the only disadvantage of those is that you don't hear the heartbeat early on - but that won't affect you now.
Hi I got the Hi-Bebe fetal doppler for about 80 euros and it was great. I used it everyday and heard the heartbeat straight away each time. Highly recommended.
I got mine from eBay for $70. It's 3 MHz by Sonotrax. It's called Sonotrax B Pocket Fetal Doppler.
i guess your talking about the heart dopplers? if so i rented one from babybeat.com and they have really good quality ones for cheap. the one i got was 27 dollars a month & we heard the heartbeat as soon as we used it. :)