AGM is known for making some alright WW II guns for under $200, however youd need to settle for the sten, or the mp44... Their mp40 is alright to but then (with german weapons) youd have to do a OSS/ FSSF load out. That gives you some leway in uniform though. The newest Cyma thompsons (without drum) shoot well and are a good TM clone. You can pick them up on CL for about $100 sometimes. The drum version while cool, is partially inaccurate due to body/bolt designs/changes. For $100 you cant go wrong, that leaves you with $40 for a set of king arms mags, and $60 to get a ver. 6 cylinder head upgrade, and maybe a bolt, tightbore, cylinder, or piston even.
AGM is due to have a BAR out sometime for $300, a copy of the VFC one. The hexagon PPSH has most of its problems fixed and mid cap drums do exist for it now. Its pricey at the $300 mark too however.
A guy on the WW II airsoft boards offers M1 Garand AEG conversion kits in 2 styles for the m14, and will build you one too. One kit is all wood, while one kit is wood with some resin made replacement parts for wood. This offers an economic version of the kit. The gun uses m14 mags shortened and comes with 2. Instructions on how to make more magazines are included and you can purchase more i believe.
Alot of the gas shell k98s are crap, and i dont hear anything good about the m1/m2 carbines or gas garand. All use 8mm, hold realistic ammo amounts, and the m1 needs to be cocked every time, the m2 does not though. Tanaka makes a cool gas shell trench gun, but picking up the shells would suck and its harder to find now.