What is the cheapest way to travel to Panama Central America by bus or train from San Antonio Texas?

I would like to travel to Panama sometime this year. I was wondering how much it would be to travel from San Antonio, Texas to Panama Central America by bus or train? Has anyone ever made this trip? I googled it but cannot find an answer. Any websites? Tips and info? Thanks!|||Theprice is about the same buy I would pick train since it's a lot faster because of traffic, stoplights, ect.