The rake on the Merge network is rather low compared to many live games.

The rake table they use can be found here: Poker Rake - CarbonPoker

If you are playing heads up, or short handed the rake will effect you much worse then if it's a full table. If you're really worried about rake then I would highly recommend just playing tournaments. The rake cost can be covered easily with a good placement in the tournament. However, you also have to weigh the risk of having your money tied up in a game where you may get no return. At least in a cash if you're running bad you can stand up and move to a new table.