A constant current supply whilst being the best for anodising will also work out the most expensive or difficult to make.
If you have a 12v supply of some sort capable of supplying a few amps (3 should be plenty) then you simply add 12v car lamps in sereis to adjust the current.
As the surface area of the part will also effect the resistance of the circuit, from my experience is that you don't really need to worry too much about measuring and adjusting the current. The supply i use is rated at 3A and has a 12v lamp in series, i just connect up the circuit and leave it for 3 hours (check every 30 mins or so to make sure it's not done anything stupid).
Your best bet is to get a few scraps of ally and try it, see what happens and modify your setup until it works reliably.
If i can iron out a few issues in my latest project gat may get round to anodising it this week, will post up details if i don't fry it