Buy a Ruger 10/22 standard model, nuthin fancy, then buy a conversion kit to make look like anything you want. The rifle will probably be about $150-$250 then a conversion kit will be anywhere from $60 to $800.
GSG makes a few tatical 22 rifles and they run between $450.00 and $550.00.
Keltec has a Bullpup design as well as S&W and Sig. The 10/22 is a good deal and there is one available with a tactical stock as well as other dealer exclusive ones. You could also just buy the 10/22 sporter or carbine and get some hi-capacity aftermarket mags for it. You can get them in 25, 30,40, 50, as well as 75 round drums !
GSG definitely has some cool .22s, I've got the GSG-5 which is an MP5 clone in .22 and it is loads of fun and like $400. It is a solid gun, pretty accurate, good weight to it, cheap to shoot, and looks cool as hell.
Here is a link to Impact Guns which has a variety of GSG guns and accessories for you to look through, as well as many other cool .22s and accessories.