-peru: are you only going because of the inca trail? if so, don’t go.
-costa rica: if a lot of people have been there, then a) it’ll be like mexico, touristy and b) it’ll be accommodating
-panama: to me, if you had to pick just one this seems like the winner. other than being the rustic costa rica, because it might not be as touristy it might actually be cheaper! also, if it’s like the panama side of florida then the beaches should be AMAZING (white, soft sand).

OR CONSIDER THIS: i’m not sure how long it would take but couldn’t you drive/bus it to costa rica for half of the trip? there seem to be a lot of costa rica and panama travel itertineries, so i know this might not help – but i think this would actually be my pick! it’s the best of both worlds and that way you’re only eliminating one of your options, AND you’ll have more options to pick the lowest priced flight. AND if one of the countries didn’t work out, then the other will make up for it. and it seems, with your traveling woes this might be the perfect way to go

p.s. i just did a second of research and this is the first thing i found on costa rica: “In some areas of Costa Rica children are given coffee in baby bottles.” i thought you’d like that.