Timely failed to mention that no. 28 is expensive mainly because he's hoarding copies. Maybe he'll sell you one at a discount to get you started, though.
I've been collecting them on and off for about 20 years. They haven't typically been that expensive. I think someone with deep pockets was trying to build a run in 2016/2017, and that drove the prices up temporarily. With niche titles like Catman, prices can be very, very volatile. It only takes one or two collectors entering or exiting the hobby to have a significant impact on prices. I buy them to keep; if you decide to pick some up, accept that you might not be able to sell them for as much as you paid. These are the ones I have:
The no. 20 was the most expensive one even though it's the lowest-graded copy out of the bunch.