If you can find a feed shop locally, or a place that sells saddles and such, you can get farriers rasps for less than 20 bucks. Place down the road from me sells em for 12 dollars each, brand new, and they cut like a dream compared to what I used before. I started off using the short Nicholson rasp/chisel combo jobbies cause they were cheap, and I remember thinking that was a good deal - I mean I got 4 rasps in a package and I'm sure they will work right? They sucked, horrible for making bows with, just horrible. I didn't know how horrible until I got a Nicholson #49 in a trade, I threw those other ones in the trash after using the #49 for about 20 minutes.
Point being in all that that a good rasp will make your work so much more enjoyable. You don't have to spend a ton of money, but spend some to get a good farriers rasp or a good cabinet makers rasp. You won't regret it.