Flexible,
You got some good information above from Nightlord, Tark, LoonWulf, and others above. I'm a a little late to the party but I would concur that the approximate value is around $800-1000 even for a mixmaster rifle. Not that you want to know, but even original finger groove WWI era stocks have become pricey bringing over $200 in fairly bad condition as well as the Sedgley USMC marked barrels bringing at about the same or more for people that want to restore their rifles to a particular specification. WWI high number receivers that have not been D&T and otherwise monkeyed with also bring around $350-400 alone. And that leaves out all of the assorted barrel bands, buttplaces, trigger guards, etc. which are not stamped metal like the 1903a3's were. I would do one thing though, swap the 1903 follower for the 1903a3 stamped follower--keep the original. The stamped one often feed better in 1903's.
BTW, if you can get used to them and have good eyes, the 1903 sights are target grade using the apertures. Probably some of the best military open sights for target use ever made. They have the potential to shoot about as accurate as the average 1903 at decent ranges. If you have bad eyes and wear glasses, then they aren't so good. If the 1903 bore is a bit worn, try using flat based bullets instead of boattails. There are micrometer sight adjusters available but they can be pricey--P.J. Ohare micrometer sights are the most common.
Both the 1903 and the m48 are also good rifles for cast bullets and you might find some surplus (albeit corrosive) 8mm Yugoslavian issue ammo still around that is decent stuff. The commonly available Prvi 8mmx57 ammo that you can get from AIM surplus and other places is lightly loaded and will not shoot true to the issue sights being quite a bit slower. Prvi does load a hotter 8mm Mauser cartridges but you will have to shop for that one. S&B is decent as well and loaded hotter (https://www.sportsmansguide.com/pro...er-8x57-js-196-grain-spce-20-rounds?a=1583557 ). This should come closer to matching the open sights on the rifle.
