According to this thread [0] the recommended fee is 0.0001 BTC that'd be $0.20. Of course if you have a non standard transaction the recommended fee will vary.
[0]: https://bitcointalk.org/index.php?topic=245552.msg2618635#ms...
> assuming you want it confirmed reasonably quickly
Generally it takes 10 minutes to mine a block so even with a very high fee you won't have it accepted in seconds (except for a pure luck situation where you send a transaction, miner takes it and immediately finds a block).
Personally I wouldn't think fees are a big deal now that miners rely mainly on coinbase transactions (getting BTC just for mining a block). Fees will play a big role when miners stop creating BTC out of thin air and will have to survive on fees only.