The Times today has an interesting (and sad) story of the sale of a collection of old books (pre 1800) by the Diocese of Truro (here). The basic story seems to be that the Diocesan Library discovered that no one had used any of the pre 1800 books for more than ten years, so they sold the lot in order to free up space. The problem being that they sold that lot for £36,000; but the lot was worth more than £500,000! The source for this is an article in the Bookdealer (here), which has some nice photos and prices.
Erasmus 1516 first edition: sold at auction for £19,200
Complutensian Polyglot (all six volumes): sold at auction for £69,600
1) Every now and then just visit old libraries and ask to see their old Bibles (otherwise they'll think no one is interested and sell them).
2) It is possible (occasionally) to make money from a knowledge of old Bibles.
3) Collecting old Bibles takes fairly big league finances.