A 4990 refurb would be excellent value for not too much money.
Prepare a time budget for the project. Think about how much time it will take you to do each scan - not just the scan acquisition, but also any negative handling and any post-processing needed. Think also about overhead for developing and implementing a labeling and filing system so that somebody else can actually find them, realize what they are, and make good use of them at whatever point in the indefinite future.
You say there are hundreds of negatives. Are you prepared for the project to take a few hundred hours? Spread over how much time? If not, is there a way of prioritizing a subset of negatives that are especially worth the trouble?
If you think it through at the start, the odds are higher that you'll scale it in a way that's practical and complete something coherent and useful, rather than running out of steam in the middle with a partial set of scans.