No there are no "cheap" night vision options. Clip ons to add to your scope run at least 7k. A cheap option would be a pvs-14 mounted to your weapon. 400yds is going to require gen3 so about 2500 plus an eotech plus a 3x magnifier which is good for .223. 300aac about 2900, and 308 about 4200. There are some new CCD Nightvision options such as the DFA-75 for a couple grand but 400 would be pushing it. Go rob a bank and them come back with your questions. Lol
Actually the WASP is probably going to be your best option for 400yd at $5k I believe. It's not out yet.
Are you hunting hogs in Indiana? I'm from Indy and would love to know of a spot to hunt hogs.