No need to spend a lot of money. I bought an Epson 2450 for $100 w/ shipping included and it works fine for what you're talking about. It also works well for scanning my 4x5. Anything under that it's best used just for contact/proofing purposes. My workflow is to take the MF or 35mm negs, develop them, scan them on the Epson, and print the keepers on an enlarger. I assume that's your plan. It came w/ a software CD that includes Silverfast as well as the Epson scanning software.
Oops, I just noticed you plan on using a film scanner on the back end. Same difference though. The 2450 will work fine for your intended use.