prices on the OP gun could be anything from $199 to $1000 honestly.. there are a lot of unknown variables..
which LR Mauser is it? German factory with pre-war serial numbers? Or a VZ24? or something made during peak war years (likely much lower quality steel and much lower quality fit/finish).. Chilean/Brazilian/Argentine? etc..etc..
how much work other than the cutting down of the stock has been done already? Since its sporting a scope, Im assuming the bolt handle has been reforged or replaced. Do you know which technique was used?
Does it still have the original mauser flag safety? Or has that been replaced? If its got a slide safety of any type its likely also got a different trigger in it than the original .mil trigger.. if so, who made the trigger? if no slide safety, does it have a 2 position or a 3 position wing safety? Or maybe a "45" safety (flips up and down at a 45 degree angle beneath the scope)..
Since its 7.92 caliber Im assuming its still wearing the original military barrel?
If the only work that has been done to it is the stock reshaped and it got drilled and tapped for scope mounts, and its not a particularly great action to start with (during the war german build, etc) its most likely a $200-$250 gun around here... if anything else has been done to it, or it happens to be a particularly great action (a mid 30's VZ24 for example) it could bump the value anywhere from an additional $50 to an additional $500+ IMO.. it really just depends..