There are a number of sellers on E-Bay who buy complete radio systems and then part them out for fun and profit. You will often find digital sport servos available for far less than retail. I bought my Ace Staudacher S-300 ARF from a seller named mnhobbies who frequently sells JR, Futaba, and Hitec radio components. You can find his items currently for sale listed here:

http://search.ebay.com/_W0QQsassZmnhobbies

I wouldn't be me without mentioning something from Ace Hobby/Thunder Tiger. Don't forget about the Ace 1903 standard servo, part number ACE8114, available for $11.37 each from www.infinitehobbies.com. With 41.7 oz-in at 4.8v with .19 speed to 60', the Ace Hobby 1903 standard servo is another good choice for a high quality standard servo. It comes with all of the usual mounting accessories and a variety of servo arms from which to select.

The metal gear version of the Ace 1903, part number ACE8121, will only set you back $12.91 from www.infinitehobbies.com and the performance ratings are the same as the standard version of the servo.

Ace Hobby and Thunder Tiger products aren't always the most common items at the hobby store or the flying field, but they're always well-made and they always offer a good value.