The electronic boost controllers are more popular than the manual boost controllers for the 3/S owners.

The HKS EVC IV costs around $600.

The GReddy Profec is around $550 and the Profec B, which has a few less features is around $350.

Blitz makes the DSBC which is by far the most popular amoung 3/S owners.  It features a peak hold function and a built in boost meter.  I've seen it advertised for as little as $400.

The Apex AVC-R and SARD are other electronic boost controllers.  The Apex unit is another popular model. A new Apex AVC-R has come out with a graphic display that is very popular.

Blitz DSBC

HKS EVC IV

Old Apex-i AVC-R

GReddy Profec