Mexico is really very lax about what you are allowed to do while in Mexico on an FMM and the fee for one isn't very much at all. But what you can't do is stay past the departure date on the FMM which cannot be more than 180 days from when it was issued. INM agents used to be very willing to just put the full 180 days on every FMM but lately are asking questions about your return plans and only giving you shorter time periods. Apparently there were a lot of people who were living in Mexico and basically going to San Diego at the end of their FMM, staying a few days, and then reentering on a 180 day FMM to return to where they live. This has always been against the rules but I don't think INM really cared that much until recently, because the number of people doing it increased greatly.
costa rica visa is 90 days maximum for starters
'expats' are very entitled; they want all the conveniences of a 'third world country' (they will call it 'shithole' when their n-th consecutive entry is denied) they want all the cheap rent;services;food ; they want to use the roads; sidewalks; beaches; national parks; police; emergency services but god forbid you ask them to pay income taxes as a local if they are going to work from their host country ' it is preposterous; i already paid 10% vat on my 2 dollar frapuccino'