from what i gather, it sounds like you are trying to stay under the $80 dollar range to be able to get the brush, hose, and color cups needed. however, i would go with a gravity feed model if you are using it for strictly model painting, that would eliminate the cups. it also allows you to spray at lower pressures thus cutting back on the overspray, plus, i helps achieve a finer line. check out the iwata hp-cr and the omni 4000. i have an omni 5000 which is the same as the 4000 except with a smaller resevoir, and it will do all that a modeller can ask for.
but, i can't let you go without saying that if price is no matter, the iwata eclipse hp-cs is the best airbrush i've ever used out of the box. it sells for $105 and an iwata hose is around $18. yes, that is a little steep, but it was well worth it to this modeller. later.
BTW, by the looks of that mig you have on your sig, you dont need an airbrush!!! nice job!!!