how much should I pay for 2x2GB RAM/is it worth upgrading my early 2009 mac?

You could get a Hybrid hard drive!  I got mine from OWC.  Just type in Hybrid drive for a search from macsales.com.  The drive has a small SSD and a tradtitional hard drive.  The small SSD loads stuff recently used.  It is VERY fast, and has more storage than a standard SSD.  It is also cheaper.

No doubt, UPGRADE the RAM.  You should start saving money for a new machine though.  If you upgrade your 2009 model, you should get 2-3 years more use out of it.  Save $50 a month or so during that time, so you can get a new machine without breaking the bank.

I tried the Macbook Airs at the Apple store, and was VERY impressed with the size and speed.  When my Macbook dies, I will look HARD and a Macbook Air.

Kevin