Do you mean it's a 240 GL manual? I don't think there is such a thing as a GLM. Unless you mean GLE?
An '82 in manual is a good combination of year and transmission. 240s aren't super rare yet so the biggest factor will be how good the body is. If it's straight, no major dents, free of rust, paint in good condition, you'd probably land somewhere north of $5k but if it's rough you'd more likely land somewhere from $1k to $3k.
If it is a GLE and has all the optional extras you'd probably get more for it as early 80s GLEs are I think pretty uncommon.
Just my thoughts. Really a picture tells a thousand words with these sorts of things, and it is a small market so sometimes you have to wait for the right buyer to come along.