Aluminium frames can be resprayed or powder-coated just as easily as one another.
Many painters or coaters will quote a price which includes stripping and prepping the frame. Just make sure that your aluminium frame doesn't get sand blasted or caustic acid dipped, as both will remove the paint but also damage the frame.
Aluminium frames can be media or bead blasted,which essentially means that soft plastic beads are used instead of harsh abrasive sand or grit.
To save some cash you could strip it with Nitromors and alot of patience. Be aware though that the metal will have to be completely free of any paint or residue before it can be coated. The main tubes are easy, but I've had to resort to a soft copper brush mounted in a Dremel to clean up the welds and various nooks and crannies on aluminium frames.
To be honest it's easier just to get it professionally stripped, as it's not really cost effective to do it yourself unless time is a luxury and you like a challenge.
Most specialist frame painters and builders like Bob Jacksons will have alot of experience and know which bits of the frame to mask off. They will also be able to accurately check frame alignments too.
Industrial powder coaters can be considerably cheaper, I've paid as little as £20 for frame and forks, but make sure they know that threads etc will need masking off. You could do that yourself too before dropping it off.
Quality can also vary considerably so it's a good idea to go for a company who has been recommended.
I might speak to my contact at Bob Jacksons & see how much we're talking to get it done. Have to say I was very happy with the paint-job they did on my last frame.
I took an unfinished frame I bought cheaply on eBay to a local powdercoaters and subsequently had issues with the bottom bracket threads. They had been recommended for bike frames but I guess they either didn't do a great job of masking the shell or it was an issue with a "too good to be true" eBay frame (seller claimed they were made by Dawes) and the BB threads were dodgy anyway.