My advice for beating Level 26 is to start playing it as soon as you beat Level 25. Your level cap would have been just raised to Level 60 and the Agents give a huge amount of Exp. That means that by simply killing 4 or 5 agents with the Anti-Freezer, you'll gain a level and get back ALL of your health and focus. Plus, once the Anti-Freezer gets maxed out, it can kill agents fairly easily.
Lastly, the one perk you should leave out is the Chainsaw. You can buy it for 1000 gold and its a pretty crappy weapon anyway.
I thought that this was a pretty great game, but once you reach the last 5 levels, it becomes a bit of a hassle. It takes forever to figure out how to beat the level, and even if you use the walkthrough, it's still relatively difficult to follow. Nonetheless, it deserves at least a 4 out of 5 : D
 "Fade"){kind=icon}
 "The Final Death Wish"){kind=icon}
 "Continuity"){kind=icon}
 "Infectonator : World Dominator"){kind=icon}
 "Finding my Heart"){kind=icon}