FWIW, Nicole, I've found KEH Camera Exchange (http://www.keh.com) to be a fairly good price indicator. Their prices will be somewhat higher than what can be found on eBay, but their condition ratings are conservative, and they have a decent return policy.

KEH is showing a range of $850-$1,300 for the 35 'Cron, around $1000 for the 90mm Cron, and $400-$1,000 for the 90mm Elmarit.