AngelSounds Fetal Doppler got my lo at 7w1d! Doesn't count hb tho. It's about £15 ish in the UK. I know people sometimes ship it over to US as it's still cheaper or try 2nd hand.
I have one that was $41.50 It works great! Bought it online. I have the 3MgHZ wand. Heartbeat rate isnt really spot on...but you can hear the heartbeat really well. I use it every other day to check on baby.