Hi Martin
It was me you compared with!
I run a KO 2123 - metal geared. Picked it up on ebay for around £30. I also run one in my 4wd, again a second hand one.
KO servo's are pretty bullet proof, especially the metal geared versions. I have one from around '93 that still works fine.
I wouldn't spend £80 on a new one as they are so reliable. But as Chris said, it is worth spending money on it if you intend to compete seriously. They will last you several years, and it will help you correct slides etc much quicker without losing the back end.
This one looks pretty good. But see if you can pick up a 2123 if there is one knocking around!
http://cgi.ebay.co.uk/KO-PROPO-PS-21...QQcmdZViewItem
ps, hope your little boy enjoyed the micro!