From a page inside this lovely book, Found, Free, and Flea by Tereasa Surratt:
Unless you happen to be in town when the Antiques Roadshow visits, most folks wont seek out professional appraisal services for their antiques. The trend of online appraisals has been catching on for its convenience, speed, and affordability. Here are some of my favorite sites:
Whatsitworthtoyou.com offers a wide range of appraisal services, from cheap entry-level appraisals to deluxe and express services, plus resource directories, courses, and more. This site even offers a “collection appraisal” service, which comes with the era, description, condition, appraiser comments, current fair market value, and replacement costs.
Antiqueappraisals.net offers a more costly approach, with fees starting at more than $120 per item, which gives you a detailed itemization of the value, how the appraiser reached the conclusion, and all the comparable items similar to your item that have been sold in the past based on the information in the site’s database. It might not be the ideal site for the “found, free, or flea” items, but it’s good to have on hand when you find that uberspecial antique in Grandma’s attic.
Oldandsold.com With a fee of ten bucks or so and less than four days’ turnaround, this site is hard to beat. And you can even search its past auctions for sold values. This site offers a ton of information for nearly all aspects of collecting.