You can get a quality G36 for a very respectable price. Used Classic Army G36's sell for ~$400, and a new Umarex G36 will go for $500 flat.
You don't have to go overboard if you want quality, used Tokyo Marui MP5s (Still quality) can be found for as little as $200.
A full set of ATACS will run you ~$100, and another ~$100 for a basic rig and pouches if you need them. Mags and batteries will cost ~$100 Minimum.
Combining all that (Used G36 and all the gear), you're looking at at least $700 to get ready to go. Yay...