Dirt Rider Magazine

So I just bought an 06 CRF250R. I want to ride on the Silver Lake sand dunes this summer and maybe some other state land, so I'm going to need to get some spark arrestors for my dual exhausts. I've seen the Pro Moto Billet end tips that have spark arrestors in them, but they run around $200 for the pair and I really can't drop that kind of cash. I've seen you can buy only the spark arrestor screens for around $15 apiece, so my question is; has anyone found an alternative to buying the whole end tips and be able to run on state land? I thought maybe it was possible that I could buy one of the replacement screens and modify the ring around it so that I could drill out a few rivets on the OEM tips and mount it on some new rivets... not sure how well that will work or if it's even possible. Any solutions/ideas would be much appreciated