The SA in a box is a Finnish arsenal stamp - meaning it was captured by the Finns during the Winter (Finland-Soviet) War. SA = Suomen Armeija
The markings are as previously noted for an Izhevesk rifle, 1909. The bow and arrow on the receiver is an Izhevsk stamp. The peened eagles are Imperial Russian markings, obliterated by the Bolsheviks.
For $125 I think you done pretty good. I've seen comparable examples (but all matching) as high as $250. You done pretty good.