For my money, Cozumel is the best value/diving combination in North America or the Caribbean. I have done many solo trips to Cozumel, and if you really want to dive, and don't care about luxury accommodations (just what are you going to do in your hotel room other than sleep?), and are willing to learn just a bit of Spanish, enough to order at the locally owned taquerias, you can stay there really cheap and spend your money on diving. Package deals at Scuba Club Cozumel are available that include food, lodging, and diving, but I was always the more adventurous type, preferring to go ala carte. You can find hotels for as little as $30 US a night (many years ago, I managed to stay for less than that -$24 US a night, but I don't know if that's still possible). In July, 2012, I stayed a few nights at Hotel La Casona Real for $43 a night, INCLUDING all taxes, and that was far from the low end of Hotels I've stayed at in Cozumel; it even has working AC and a pool. It's about 2 blocks directly back from the Plaza, easy walking distance to the Plaza and many downtown restaurants. You can get up early and walk to the Zermat Bakery for Coffee, Juice and pastries for breakfast (or buy your pastries the night before), then catch a dive boat from an operation that leaves from a downtown pier. Aldora leaves from downtown, but it is one of the more expensive Dive Ops; I really like it because of the HP Steel 120 tanks, LOTS of air, LOTS of bottom time, and long SI at a beach club. But if you shop around and negotiate for a multi-day dive package, you should be able to find a Dive Op that leaves from downtown (or will cover the ride to and from the Caleta -- that's the marina where most dive boats start from in the morning -- its well south of town, and a hefty taxi fare if the boat doesn't come to your hotel or a downtown pier to pick you up) for $55-70 US a day for 2-tank boat dives. And there are lots of very good places downtown where you can eat cheap. I would typically budget $40-$50 US a day for food, but you could easily get by on as little as $25 a day if you like Yucatan food and were willing to eat at the cheap local places - the food is still damn good. As an example, I would eat a late lunch after returning from the diving at one of the local Loncherias that offer Comida Coridda (literally, "meal on the run"), a fixed price meal that includes chips and salsa, soup, an entree (chicken mole, enchiladas, fish -- there are usually at least 2 choices, often several) served with rice and beans, and unlimited agua fresca to drink, for 70 pesos - about $7 with tip. Then, for a late dinner, visit one of the many Taquerias along Ave. 35.
Do not be afraid of the currents at Cozumel. Cozumel has lots of very fine dives appropriate for beginners. It is drift diving, meaning you drop off of the boat, descend to the bottom with your group, the Dive Master will lead you through the dive, and you just let the current carry you along. If you can learn not to fight the current, it's the most relaxing diving there is. And the qualty of diving in Cozumel is unmatched -- clear water, incredible visibility, abundant sea life, magnificent coral structures.
---------- Post added August 10th, 2013 at 01:17 PM ----------
I just got done checking on Hotels.com, and you still CAN get a room in Cozumel for $24 US a night -- at Hotel Posada Edem, downtown, North of the Plaza, about 4 blocks back from the Ocean. On Hotels.com, it is $168 US a week. ad 14% for tax. For a nicer place, try Suites Vima, a very small (12 rooms) hotel North of the Plaza, about 2 blocks back, right around the corner from Zermatt Bakery, at about $35 US a night, and it has a pool! So, figure $40 a night total for Hotel, $40 a day for meals, $75 a day for diving (that's $60 a day for Dive Op and $15 a day to tip Captain and DM), and $20 a day for taxis, drinks, misc., that's a budget for everything except Air of $175 a day, or $1,225 a week. And you can go cheaper, as I pointed out above.
---------- Post added August 10th, 2013 at 01:19 PM ----------
Whoops - I overestimated. If you stay for 7 days, you will not be able to dive 7 times. Only budget for 5 or 6 days of diving. So subtract $75 or $150 from above estimate.