Buying old domains depanding on online domain lists and rankings is not too efficient usually this data is not actual. To buy good old aged domains you must quickly grab the ones that are expiring in upcoming days there are thousands of expiring domains so the only thing you need is to quickly and preciesly get actual metrics about them, important can be first registration at web archive (to know how long the domain is indexed in internet) and search engine metrics like Site, links and backlinks to estimated SEO value of such domain. Next you can check alexa rank to approximate the traffic. And you are done domain with highest metrics is the most worth of buying and can guarantee that will have a traffic and will be usable for increasing seo reputation of your other sites. Otherwise you can also sell such domains for a profit. I strongly recommend you checking eXdomain tool that enables you to verify mentioned metrics for almost unlimited amount of domains simultanously in one day. There is also posibility to download dropping domains lists directly from the application that are retrieved from most popular providers like justdropped or godaddy. Look here for more information: http://en.exdomain.eu
The true is that it's not too cheap but mostly it's the reason of the fact that with the product you get access to all future updates that are mostly based on users suggestions, so the tool constantly adapts to your needs.
Ya here you can get some, but remember old domains can have added value, so you may need to pay more to get aged domains.
Yes, and as the value is higher owner will ask for more money. Buying old domains from owners is ok but only if you need exactly particular domain name (for example related to your company) then you have to pay the guy to get it. But if you need just old aged domain the best way is to catch them for example using the software like eXdomain which I have mentioned 3 posts earlier.
They can be pricey, but try the bst trade section or flippa. If you are looking for more expensive names, try sedo
Any other sites which can help in getting good PR domains. I tried to search on google but didnt find satisfying results
You can sort GoDaddy and NameJet PreRelease names by age here: http://genericdomainfinder.com/godaddyauctions and here: http://genericdomainfinder.com/namejetauctions As long as you buy the names through a backorder, you'll retain the creation date age. If you wait until the domain name drops, it will be re-registered as a new name with a creation date of 2012.