Anyone eligible for Rule 5 who isn't on the 40 man, and isn't one of 38 guys protected beyond the 40 man can be taken for a small fee and only costs the $12,000 fee to draft him. There are no roster requirements on these guys for the drafting team(other than placing him on the 38 man AAA reserve list I assume?) Considering you can protect up to 78 guys, and it's rare that somebody is protected when not eligible for rule 5, you're looking at guys outside the top 50 prospects of a team.