Cashing in a re-buy without re-buying?

[redandblue]

Is this hard to do? I was thinking of playing the $3 re-buy 25K guarantee a few times, but my strategy is not to re-buy, as i only have a small BR.
All i have to do is get in the top 500ish then i will get like $21. It sounds like a good deal to me, and i might even get lucky and make it deep once or twice, that would be great for my BR.
But, will i have to build my stack so big that I'm better of playing regular tourneys?