I bought a 38# Tigercat in a pawn shop for $20.00. Don't let that throw you because I got a G R E A T deal on that one. One of my better finds. Depending on what year, and what wood is in the Riser, it very well is probably worth $100.00. Your serial number says 1968, so that is a plus. 53# is uncommon in a Tigercat, so that is another plus. They are great shooters (+#3).
As a shooter, or hunting bow, I would think he got his monies worth. As a collectible, it would depend on the condition. If it is in average condition, and not beat all to heck, I would say he did ok.
A good guide is to go to eBAY and see what is up for auction. You can also go to "Compleated Items" and see what they have finished at. i ams sure that some went over $100.00 and some did not.
I know one collector that is hot after a '68 Tigercat if it has a Shedua riser. I think bear made them in three different years that year, and he needs a Shedua riser to round out his collection.
Tell your Buddy that if it is worth $100.00 to him, than he did OK, and not to worry about what someone else thinks of it.
Traditional Bowhunter magazine this month has an article called "Part Two of the GREYLING BEARS" It gives a good history on the tigercats, and is very complementary about them.. He should pick up a copy.