Don't skimp on getting cheap components! Bite the bullet and spend extra- I've tried being cheap in the past and it's just not worth it in the long run.
Mixer wise look at Behringer Euroracks- The newer MX2004 seems very good value with it's 8 mic channels and 4 stereo channels.
The Mackies are a lot more expensive, but as far as I am concerned they do sound better- better preamps. However, I reckon you are better off looking at the Behringer. I myself own an MX2642 4 buss rackmount which is great for keyboard sub mixing with it's 26 inputs.
Check out the new Alesis M1's for cheaper good quality powered monitors. Also Yamaha MSP5's I heard are good as are the Event 20/20's (active versions).
You wont be able to understand how you were able to monitor through your hifi after listening through a pair of dedicated monitor speakers! Hope I have been of assistance.