Christopher-

The M. Thys sounds nice, can you post photos of it as well as the Mahillon?

Although Bramble makes the point that your price range plus some could get you into a brit rifle, the work of M.Thys is considered among the best, and I can imagine this Griffnée engraved example is spectacular.
If it is in the 'as new' condition you note, it sounds like a good price.

If the Mahillon really is tight on face and without mechanical issues the price for it sounds good too.

Let's see some photos!

--Tinker