Any of the early Tamiya models like the Panzer II are cheap and easy builds. I see that Italeri re-released their Chaffee which was a nice kit with decent detail and cheap. OD is all you need. Their Sherman was pretty cool, but might be hard to find.
Check the internet companies rather than your LHS, you will be able to get a kit you probably didn't think you could afford.
www.greatmodels.com or www.rollmodels.com have competitive pricing and good service.
"It is well that war is so terrible, lest we grow too fond of it."-R.E.Lee