If domains are real estate, then the same rules of real estate should apply. In real estate, taxes are based on the value of the property. So, a person asking $10,000 for a domain shouldn't be paying the standard $15-30 renewal fee as a person asking $200. The renewal fee should be based on the domain's value. Domainers want to claim it's like real estate without applying the most fundamental rules of real estate.
Your course of action really depends on how much work and effort you can put into the expired domain. If you're barely able to maintain and optimize your current site, you probably want to just 301 redirect the old site (note: see my amended comment above about the link value not likely to be passed). If, however, you're more creative and have some time on your hands, you can try your hand at crafting a microsite. If you really know your stuff and are experienced at making money off various websites, you'd probably do well with the third option.
Most popular auctions with expiring domains are at godaddy, namejet, snapnames. Search for expired domains name its very easy if you have domains list. With a bit luck, you can drop good one with PR5 cheaper like $200, just need to know which domain have not fake pr. List of domains are not free, but updated dailly with aprox. 50.000 new expiring domain names.