Macs are pretty good value. Official Apple upgrades cost a bomb though.
I upgraded the RAM from 1GB to 4GB. 4GB cost me about $90. An extra 3GB upgrade from Apple would've cost $300. It was Corsair RAM (you don't get a better brand for RAM) and saved a cool $200+.
You could do the same trick with your hard disk or processor even. For example 1TB hard disks costs just over $100 nowadays, whereas Apple will charge you at least $250.