For EME at 1296MHz with a 5m dish, we need better than 0.5 degree pointing accuracy.

And, we will need to re-point the antenna every three minits.
The world moves 0.25 degrees per minit. The moon, 0.01 deg/min.

There are Arduino projects on Sourceforge and the HRD Forum.

Using stepper motors, and gearboxes with known ratios, this is easy.

eg. 96 step stepper, 15:1 gearbox, 50:1 main worm drive.
96 x 15 x 50 = 72000 steps. / 360 = 200 steps per degree.

How good is that?

Stepper Motors with controllers search eBay "NEMA stepper".
Gearbox: an eBay search for "worm gearbox" is very dissapointing.
Mounting them and using the output shaft is difficult.

Have a look at this catalog: http://www.unixservice.com.au/hamradio/rotators/WangyeWorm.pdf
A mate brought in five hefty ones, 35mm thru shaft, 50:1, for less than $100 ea.
These can be easily mounted, mount holes everwhere.
Are you interested?
alanb (at) unixservice (dot) com (dot) au