I have a doppler for sale. I bought one and then a week later a friend loaned me hers. It's only been used a handful of times, if that. I can say it works great and I found the heartbeat at 10 weeks
It's this one:
https://www.walmart.com/ip/Easy-Home-SweetieSong-Blue-Pocket-Fetal-Doppler-100S6-Baby-Heart-Monitor-Kit-4-pc/50350686
$25 shipped in the US.