IMO - if you expect to be in high demand (sophomore recruit type kid) as a pitcher you better be 90 plus or have a frame that projects it easily.
if you are comfortable as a stand by guy (JR year recruit or SR summer) waiting for the higher velo's to shake out and then see what spots fall between the cracks - you can get by at the 88 range, slightly lower as a lefty but not much.
below 88 you aren't going to get the time of day from any D1 - I have watched many many pitchers in the 84-86 range just get people out repeatedly and there is little to none D1 interest for them.