If you want a very precise value estimate and description of its configuration, you will do no better than the CMP forum.
If you want a very coarse, inaccurate professional opinion on paper for an insurance company, you will likely need to pay some hack gunsmith to print something for you.
The quick an dirty way to value it would be to search gunbroker. Determine what you have, then search the completed listings. These figures tend to be the highest that market will bear.
All that said... an 1903 or 1903mk1 in their best shooter forms rarely bring more than $500. If it's a Rock Island from the "bad heat treat s/n range", it should be considered a wall hanger at no more than $300. If it is a drill rifle (plugged barrel, welded safety etc), it is just parts for $100 or so. There are of course exceptions, you will get the best estimate by getting excellent macro photos of every mftr mark, and stock cartouche, and posting on CMP.