I suggest a MP5 personally, but really any TM gun will be good. M4 new version should be within your range. Try to stay away from the MP5k, as it has a really short barrel, bad range, etc.
Remember to factor in mag, BB and battery cost.
RS Type 56-1 & RS Type 97B & KWA M11A1 w/steel kit
KJ M1911A1 & KSC G19 + AI Grenade