Here's some information from some of the prominent equity/vanity/subsidy publishers. These comments are based on the information on their respective sites and the sales figures are based on the figures quoted in these companies' news releases (total sales divided by total number of titles).

PublishAmerica
Pays: 8% royalty on cover price (on first 2,000 copies)
License to publish for seven years, author retains copyright and non-book rights
Average number of copies of each title sold: about 71.

Xlibris
Pays: After $500+ setup cost, pays 25% royalty on cover price, 10% royalty on wholesale price
Nonexclusive license to publish, author retains rights
Average number of copies of each title sold: about 125.

iUniverse
Pays: After $460+ setup cost, pays 20% of net (actual receipts), royalty paid quarterly
Nonexclusive license to publish for three years, author retains rights
Average number of copies of each title sold: about 70.

AuthorHouse
Pays: Royalties of 5-15% on suggested retail, depending on cover price, paid quarterly
Nonexclusive license to publish, author retains rights
Average number of copies of each title sold: about 100.

Thus, depending upon royalty rates and cover prices, most authors can expect average revenues of about $70 to $320 minus any:

1. setup costs
2. extra editing, photography, or design costs (if applicable)
3. marketing costs (postcards, travel, long-distance calls, flyers, book tours, etc.)
4. time it took to write the book

I hope this information is helpful to those researching subsidy presses.