Welcome to the forum. Something seems amiss with that serial number, as the first M63s were numbered in the low 100000 range with the M prefix.
In general, these guns are not rare, but they are in demand and tend to sell fairly quickly when available. Condition is important, but almost new in the box it could be a $500 gun (or more!). As a well used but still reliable shooter it would probably bring about $300. Remember that there are regional effects in prices, so what goes for one price in the west or upper midwest might not bring as much in the south.
The model was introduced in 1977, so it's not older than that. If you can come back with a revised serial number we should be able to narrow it down.