I’m a relatively new diver. I started diving 3 years ago in Cozumel; resort course and then a 2 tank follow-up at Palancar Gardens. Last summer I got my OW in Coz and did a follow-up two tank dive also in Coz. And then over Thanksgiving we stayed in Playa Del Carmen and I got my AOW. And earlier this month I was on a liveaboard in the Bahamas, diving off a nassau and in the Exumas. I’ve just returned from Cancun where I got my Deep Diver specialty cert. diving cenotes.
So hearing that you’re backpacking, I’m assuming you are trying to do this on the cheap. Is that right? I totally understand, I spent $1k for the liveaboard. That was cheap. I would recommend hostels. I know they are abundant Cozumel (usually about $15 - $20 a night) and Playa. I’d imagine the same is true for Cancun. I used Deep Blue in Coz for the 2 tank at Palancar when I first got started, they were good. In Playa, I got the impression the hostels might be a little more expensive, but I love the euro feel of Playa. You can ferry between Coz and Playa (45 min / $26 round trip). You can take a bus if you want from Playa to Belize City (I think it’s a 10 hour ride.). You might also consider spending some time in Tulum. I used ScubaPlaya in Playa and was happy with them. There’s a number of good shops in the area. Then when I was in Cancun, I used Deep Life Divers. They took me to the cenotes in the Tulum area; Angelita and The Pit. It was my first experience in a centoe and it was awesome. Note, those two locations require you to be at least AOW certified. Deep Life Divers did a really good job and I’d use them again. They’re pretty close to full service. They have contacts in Playa, Cancun, and Cozumel so can be a 1 stop shop for your diving in Mex if you want. In all my experiences, the rentals have been satisfactory.
Hope this helps. Let me know if you have any questions.