I never said I was a lawyer or a "guru", but I think it would be difficult to argue that competing in a contest where you're unlikely to break even can be considered "valuable consideration", as it has little market value.
for a court to find "consideration" (which is really not the basis for getting contracts thrown out these days, anyway), it doesn't have to be valuable.
they might consider if the two sides were giving up something of roughly equal value. these days this part is rarely grounds for finding no contract . . . if it ever was.
cts are not going to tell parties how or when to contract.
the definition of "professional" has no bearing on contracts . . . the Uniform Commercial Code cares about merchants, but the UCC applies only to the sale of goods.
someone could make out an antitrust case against the IFBB . . . maybe. but i doubt lee or the PDI has the resources to pay $600+/hr. most antitrust lawyers do not work on a contingency basis . . .