At $2.50 per stone you could just visit a jewelry store and have them remounted in another cheap setting. Still wouldn't be a bad deal. As long as the stones are decent...if they look like they've been chiseled out by a 5 year old then no.
Probably have a couple grams of silver in them too...sterling is 90%. Could be close to $5 there. ~31 grams per troy oz.
Yeah, the raw materials alone make this a good deal. White topaz is normally around $3-5 per carat.
But be aware what you're getting. This deal is nice if you like topaz as a stone (as I do) or birthstone. But aesthetically, white topaz looks a lot like... glass. The item description says "fiery sparkle," which is simply untrue: topaz is near glass in index of refraction (sparkle when cut) and dispersion (fire when cut).
If you're looking for flashy-but-cheap, the best deal bar none is actually cubic zirconia. And it's cheap only in the sense of inexpensive. CZ is equal or superior to diamond in every aesthetic category; most jewelers need instruments to distinguish the two. For flawless color, flawless clarity, flawless cut at $1/carat, CZ is an amazing technology.