Donation button is cool at Leshcatlabs, but you should consider some ads to help as well. No need for nutso popup crap or popbehind stuff, just some click through or page view ads to help the signing fees etc. Justa thought.
You didn't mention which type of drivers you want to sign but Code signing certificate can be used to sign micro-soft drivers, you will just need to convert the code-signing into correct format either 32-bit or 64-bit. For code signing certificates for drivers, Comodo Code Signing Certificates are the cheapest right now and also works for various platforms, i found comodo code signing certificate at just $70/yr at one of the reseller, CheapSSLSecurity.com