So Batman is a billionaire, Reed Richards is a super smart, others have government backing..........How exactly does Punisher have all of these weapons with no financial backing? Maybe I need to read up and he is hooked up with someone rich but from what I remember it's just him.
Most of it he takes after stopping the bad guys. So like he stops a mob, then he takes the mobs weapons from their warehouses. His most recent high tech stuff he stole from HAMMER, since he knows Osborn is a villain, he figures he is just stealing stuff that has already been stolen.
In addition to just stealing weaponry from mobsters and gangsters, Punisher has also had accomplices such as Micro who provided him with weaponry, etc. He has also just stolen stuff from SHIELD safehouses on occasion. He also probably raids military weapons caches in various countries.
Pretty much Frank gets his money from all the scumbag criminals he kills. But his high tech weapons he gets from raiding SHIELD safe houses and HAMMER agents he takes down. He also has a guy in Micro, haven't been up on the latest Punisher but he's working with someone who can get him lots of high tech gear, like Antman's head thing.