We spent 15 days in CR and didn’t run out of things to do or see (fact is we missed several big things we would have liked to see). Our spanish is very limited and we had no real problems. The costs of things are very cheap. We spent about $10 a night on basic, clean, and friendly hotels. We traveled by local bus for next to nothing (Coast to coast bus ride $10). Do try and get a “Directo” bus if you can because it’s faster and easier than busses that make local stops.
You can eat for a 2-5 dollars pretty well. We packed about 4-5 days clothing and found it easy to drop it off at a local laundry for $3 a load.
I’ve never been to Belize so I’ll leave it up to the others to answer.