Well.... knitpicks just came out with a interchangeable set of acrylic needles
for just under $45. That may seem like a lot, but it gets you every size from 4 to 11 with cords to make 2 different lengths so that's effectively 18 circular needles. Or more. Big savings. You can easily knit flat on circs as well as in the round, many of us don't even use straight needles anymore. That will take you a long way toward having everything you need, and the reviews on them have been mostly favorable.