That is about as open ended a question as there can be.
So many different mausers were made in 8mm. Of course, with any gun condition can sway pricing up or down, but for 90% of them out there here are the values In My Humble Opinion.
If it is a 98k, original = that is a steal (Price could be 700 - 1500 or more depending)
if its a 98K russian capture, 275 is average
if it is a turkish mauser in great shape 150-200+ depending
if it is a turkish mauser in in poor shape 80 or less if really rough
there are some varrients that can supprise you due to collectors looking for rare guns, they were made for many countries, etc. Although, Chances are it's one of the above.