Congratualtions
What you have found is a small ring mauser made by BRNO. There were two models called 21 and 22. If you have and 22 with scope mount bases milled in the two bridges of the receviver there will be no problem finding mounts. Some rifles were built with a peep sight that were fitted in the rearbridge of the action, which is quite hard to install afterwards.

7X57 is a very popular cambering for thoose who want such a rifle and the right buyer wil pay you alot of money, depending on condition, narurally. They are very popular in USA by collectors. In Sweden they are not very popular or highly priced..

It would be great if you could post some pictures of your rifle, which side is the safety on? Don't be shy

/ JOHAN