You get 60 free connects per month. Each proposal costs 1-2 connects (except when the client invites you to submit a proposal, then it does not require connects). I've never bought a connect, so I don't know how much they cost.
Starting in May (I think), there will be no more free monthly connects. New FLs will get 20 free ones to start with and Top Rated FLs will get a one-time allotment, too. Otherwise, connects will cost 15 cents each, and proposals will cost from one to six connects each. Proposals you are invited to submit will continue to be free. There is a thread in the Official Announcements forum with details.
The UW fee is totally separate. You pay 20% of the first $500 you earn from each client; 10% of earnings from $501 to $10,000; and 5% of earnings above $10,000.
Clients pay a small transaction fee to cover the cost of processing their payments.