Most proxy networks that I've seen sell, have sold for 2-3 months revenue. This is due to the fact that a) they require a fair amount of resources and b) their traffic dies down reasonably quickly.
I have a network of proxies of 12 domains.
Sites are just over 1 month old and just using adsense they are making about $1.50 to high $4, $6, $7 day sometimes
Just in march so far they have made $62.74 just with adsense.
I applied for infolinks and still waiting for approval but i am trialing adbrite inline ad's now for nearly 48hours and its made so far $1.54 And the inline links hardly show 3 to 5 links, so it has heaps of potential if you have a infolinks account.
I am thinking about selling it and starting again... was fun so why not... what could i sell this for?