You can uninstall updates again I guess - that should give you the market back. What's happening there is that as you are S-On, your market app isn't removed by the update (because there's no write access to /system when running android), so the update is going into /data/app. Uninstalling update then still leaves the original market in place.
So one option is to try that again, then either get Ti Pro or install Astro.
Otherwise, you need to edit a copy of the ROM zip on your computer and remove the market updater from there.
Or, you could try this:
* set up adb on your computer, if you haven't already (see the ADB and Fastboot FAQ, from the All Things Root Guide sticky post)
* boot into recovery and connect phone to computer
* use the following adb commands
adb shell mount /system
adb shell rm /system/app/MarketUpdater.apk
you can check the file is gone using
adb shell ls /system/app
* I'd probably clear cache and dalvik from recovery before rebooting, just to keep things clean
What that does is use the Android Debug Bridge (adb) to issue some linux terminal commands to remove the apk from the system. Being S-On you can't do that while android is running, but when you are in recovery android is not running. You may have to run this as an administrator.