Do you like SEO contests? Do you like to be a part of big events with healthy search engine competition? Then you dont want to join the topseos contest as they just want all your money. Yes its true it costs $5000 just to signup. No word on any prizes other than "recognition as an outstanding SEO in your field" thats a lot of dough for a simple widget badge.
Maybe they mean that they will give you $5k if you sign up. I would imagine you'd pay it if it was a company huge in the field that recognition would help but if it is a relatively unknown company then no.
LOL, i take it as a waste of time, spend time with your clients and spread the word around through them, dealing with known clients and people known to them makes life easier, but winning an unknown seo contest and getting some unknown clients to do seo for, inviting trouble, expectations increase with such kind of fame.....then you need to deliver