That's a steal! It takes a little work to get the old frame off and remove all the old sealant, but the replacement frames are cheap and easy to install. You do need to know which manufacturer made it, as tanks that are nominally the same size are different enough that Aqueon frames won't work on Perfecto tanks, for example.
I replaced the frames on a 45 gallon tank recently. The new frames were $26 altogether; your tank is larger, but also a more common size, so I don't know how that will effect the price. Add to this the price of some silicone and a few razor blades, and 30 minutes of your time.