we are traveling to mexico in Apr. via air... should we expect to pay any tax or other fees at the airport, et

in my search for airline tickets I have read here and there that some foreign countries require you to pay "fees" and such for "permission" to enter the country. What should I expect?

Mexico I think the taxes are like 15 / 20 bucks

I have had extensive experience traveling abroad. The only fee I ever incurred was on departure. I have never incurred an entry fee. Most notably the Caribbean Islands have exit fees that usually run about $25 US dollars per person. I would image that you should be prepared to pay an exit fee when departing Mexico.