A few thoughts...

AA does not allow you to "buy up" status, CURRENT elite members can pay a (hefty) fee to retain status if they fail to qualify in a given year. (something like $499-599.)

The AA challenge is free, but you do not receive any elite benefits until the challenge is completed. (I became Plat on AA in 2004 via a challenge and have requalified the normal way ever since.)

It seems like the USair "buy-up" allows those without status to immediatly receive status benefits by paying a fee, even before the challenge is complete. This is a better benefit, and this is why they are able to charge cash for it.

For $200, I am seriously considering a buy up to Plat on US, particularly at this time of the year where successful completion of the challenge would get me ahead of the Gold Crowd in the upgrade queue for a full year. I will just need to get the timing right to make sure I can get the required segments in.