Daniel,
Without pictures and more detail information, it is impossible to give a very specific value. A lot depends on barrel markings, early vs. late production, factory finished vs. kit, etc.
I've paid as little as $275 and as high as $850.
The half stock Leman was GRRW's most popular and lowest priced rifle, and therefore, there are more of them out there, and they usually command lower prices today than the other models.
A couple of GRRW half stock Leman rifles have been for sale on Gunbroker since end of February for one and for at least a month for the other. The sellers have been asking $1200 and $1800 starting bids with no action. One can deduce that they are priced above market value.
For more information on GRRW's half stock Leman rifles, check out my website
http://grrw.org/leman-trade-rifle/