Ordering them online is better than buying in store. Finding the heartbeat right now will be tricky... It's best you wait till your second trimester if you really want it or else you'll just worry yourself sick if you can't find the heart beat.
I have the Sonoline B Fetal Doppler and have been able to hear baby since I got it at 8 weeks 4 days. ☺️ It costs about $40 and can be ordered online.
Also a lot of women get confused with their placenta's heartbeat (esp if yours is anterior), your heartbeat and babies heart beat.