Nerlens Noel - C, New York Knicks
If Spurs strike out on Collins, a much cheaper option would be New York's Nerlens Noel. Of course, you get what you pay for, as Noel's career has been riddled with injuries and he's only made two threes in his seven-year career.
One thing Noel does incredibly well, however, is protect the rim. Nerlens averaged a staggering 2.2 blocks per game and 3.3 blocks per 36 minutes with New York this season. He has the kind of interior presence that would greatly improve a Spurs team that finished in the bottom five in points in the paint allowed per game (50.1).
I would certainly prefer a stretch big at this point, given how much the Spurs have struggled to shoot and make threes this year. For that reason, Nerlens shouldn't be the first option by any means. Given that he's unrestricted and only made $5 million this season, however, maybe there's a way to get him at a bargain.
Bobby Portis - PF, Milwaukee Bucks
The Bucks are another case of not having much there that the Spurs need. Their free agents include 36-year-old P.J. Tucker, Giannis' brother Thanasis, another point guard in Jeff Teague, and Bryn Forbes (been there, done that).
That pretty much just leaves the 6-10 center from Arkansas, Bobby Portis. While he's not a gamechanger, his 3-point shooting for a big man is certainly impressive. Portis shot a staggering 47.1 percent from beyond the arc with the Bucks this season on 2.4 attempts per game.
For someone who only started in seven games this season, averaging 11.4 points and 7.1 rebounds is pretty remarkable. That said, he has a player option and is probably happy to keep playing for a perennial championship contender.