As said elsewhere in this forum, one of the easiest ways to get into proxies is to buy one. That way you have something already working to learn from.
Some pointers on knowing how much to pay.
1) how much have other similar proxy sold for recently
2) my favorite – look at the revenue and divide that by the sales price which will give you how many months earnings to get back the sales price. Be super careful here – many sites seem to sold off after 1 to 3 months not giving you a true picture of earnings. If over say one or two years, then you get a real picture. Many use a rule of thumb of 3-6 months earnings but if you are talking about a site that has been around for much long period of time the multiplier could be much higher.
3) think about how long it would take you to put the site together – how much is it worth to you having that proxy all ready to go?
4) Look at the traffic – does it mainly come from the high paying countries like USA UK, Australia NZ etc of is mainly from the “junk” countries?
6) Where does the traffic come from? Is it mainly from SEO work (search traffic) or some other source.
Any more ideas people?