Did a bit of research on the name, and looks like it probably does not get much traffic so I assume you are looking at just an idea of value based on the name.
The main problem is that with proxy sites the name is not as important as with a lot of other subjects ... Mainly because you are dealing with people that have a bit of knowledge.
Whilst it is quite short, the two words do not really sit together in that order.
I think that if you are developing it then the resale is really going to boil down to the quantity of visitors and the conversion rate of them to clicks on advertising.
To be honest I do not see it making much above registration fee unless you can prove income from it .... Even then it will not make as much as a site receiving similar traffic ( and conversion rates ) purely because proxy sites are a well known way to get banned from a lot of servers.
As it stands go for low $xx, develop it a bit ( get decent traffic ) and might reach the low $xxx.