cash value aside, what is the utility of both the carbine and the pistol to you. Do you need, or can you use a handgun in the caliber offered? The carbine is a deer gun (within its limitations) does the GLock have the same capability?
Is that important to you? Do you have other guns, so the loss of the Marlin won't put a hole in your abuility that the GLock cannot fill?
Lots of things to think about. Would it make a difference to you if it was a different handgun? Is the Marlin excess to your needs, and wants?
What a gun sells for on the market is a useful thing to know, if you are planning to sell the gun. Otherwise, its all about what the value is to you, in real world utility. If it was my only deer gun, I wouldn't trade it for any handgun of the same approximate market value. If I needed a handgun more than another deer gun, I would. Its all about what its worth, to YOU.