Hi, and welcome to the forum.
There are so many variations and possible issues that it's almost impossible to give you a valid pricing estimate without pictures.
Take a No. 2 pencil and see if it can loosely be inserted into the barrel. If so, it's 9mm. If it can't go in, or is very tight it's .30 Luger. I recently posted a study:
http://forum.lugerforum.com/showthre...ight=.30+luger
Is "581x" the actual number, or did you use the "x" to conceal the last digit of a numeric serial number?
Marc
__________________

Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.