Basically what Meth01 replied.
Another easiest way, is farm like crazy for fortune boxes, and save a least 100. Or maybe less. Though, more likely get something, out of 100.
Also, be ready to farm in portals. That's the another way. Fuel up.
I am a returning player to Super Mechs, and was wondering if there was a Discord server for the game, as I do not really like talking on forums. (It is ok if there is not one, though, as I do not mind)