Given the proximity of your feet to the firewall, scattershield, etc. a pair of /15 or /20 boots (as in Top Fuel style boots) are the way to go. Yes, you can drop a lot of $$$ on a new pair, but a Google search should net you some used boots in good shape. I bought a pair off a Alky dragster guy a few years ago for $200. They're out there if you look hard enough.
Remember, the rules listed for safety equipment are the minimum requirement. A couple hundred $$$ extra is worth more than burned skin, IMO.