I have an 88 samurai JX......what is the least expenxive way and easy to get a little more power. I have to go over mountain passes in it and it struggles going over them. Any ideas?

K&N air filter into your stock box... probably cheapest

Stock or modified truck? Bigger tires than stock? You may need to change your gearing. 

Throw a 2" exhaust on there and let the engine breath a little bit.

I'd suggest doing some simple checks to make sure the internals are good.  First that comes to mind is a compression check.  I'm making the assumption that you keep up on maintenance, plugs, wires, cap, rotor, oil, filter, fluids from axles up, ect?   

On my original 1.3L I had a exhaust header and oversized/less restrictive air filter (don't know who made the filter) on my 87 Samurai.  Drive line was stock.  3.5 S/R lift.  On original sized tires I can run down I-70 around 80 mph.  Don't get me wrong it takes a bit to get there but maintains real good.  When I stepped up to 30" tires that was a different story.

I agree with Drone637.  Your best bang will be breathing.  Air in, Air out.

I am in the process of swapping engines.  Going to a 1.6L 16v.