1) Should I buy the pre-paid van fare round-trip for $40 or so per person, or simply grab a taxi at the airport? The later sounds like it would be cheaper and would work just as well.
2) What are the eating options like around the pier area? Anything cheap? We're usually low-budget travelers and don't care to go to fancy places. Heck, we'll probably go to Chedraui and buy sandwich fixings for many of our meals.
Definitely DO NOT book the pre-paid van fare - that sounds like a HUGE rip off to me. Last I was there (December, 2014) the Shuttle vans from the Airport to Casa Del Mar were 96 Pesos per person - about $6 at current exchange rates - and there are always plenty of shuttles ready to go. Should be about the same for El Cid/La Cieba, as it is almost across the street from Casa Del MarReturning to the Airport, you can take a taxi - taxis can drop off at the airport, but are not allowed to pick up there - and it will take both of you for less than $10 IF you pay in Pesos. ALWAYS pay for taxis (and most everything else) in Pesos. Yes, they'll be happy to take dollars, but you'll get raped on the exchange rate.
In terms of eating options near El Cid, there is Ernestos, The Tikila Bar, Paprika, and, not too long a walk in the direction of town, the Blue Angel, which has decent food. But, while none of these are expensive places, none are what I would call "cheap eats." You can do a lot better, both in terms of quality and value, by going into town. Try any of several Loncherias, that offer the Comida del dia, a full lunch usually including chips and salsa, soup, an entree with rice and beans, and agua fresca to drink, for like 75 Pesos (less than $5 at current exchange rates), or go to La Perlita on Thursday for the 2-for-1 Lionfish Special and get the Coconut crusted fried lionfish, or Pescaderia San Carlos for lunch (it's not open for dinner) and get some great fresh seafood at very reasonable prices, or for really cheap eats, any of the Taquerias back on 30, like El Pique or Los Seras. And El Moro has a huge menu, all of it delicious, at very reasonable prices. Check out the CozumelMyCozumel.com site for good reliable recommendations on dining.