Well, they're going to have to pursue someone good and cheap. David West will likely be too expensive for the Spurs taste and therefore out of the question. Anderson Varejao would be an ideal target, but don't know if the Spurs could outlast the compe ion - especially considering his old coach, Mike Brown is trying to convince Faker management to go after him, as well. Meaning Varejao will likely carry a high price tag.
There are not very many low-cost productive options available. Clark is just as good of a PF target as any.