I've owned a few cats before, mostly brands that were locally produced
in other countries (australia, new zealand). Most of the cheap cats
you can get are small, 14' and dont have a lot of flotation. they move
along quick with one person on board, but can get real bogged down with
two. These are cheap easy to sail boats though, and they're very
forgiving. Most have only one sail so they are great for learning on.
You can pick them up for as little as $200 with a trailer if you look
around and you're not going to lose much if anything when you sell
them. It can be worthwhile buying one (or even two) of these and
putting them on the same trailer. They are super light, and can easily
be rigged by one person.

There are a couple of more 'serious' 14' cats on the market with more
flotation and a jib, and some have trapezes. I own a brisbane built
cat called a caper cat made by calypso shadecloth company who also make
umbrellas and awnings. This cat has a jib, and more sail adjustments
than most of the smaller cats (backstay tension, outhall, jib
fairleads, downhall, full traveller, mast spreader etc etc) and is
claimed to hold 6 adults. While the 6 adults would probably have to be
on the skinny side of undernourished, I have had 3 full size 200lbs
plus adults on it and it handled quite nicely. There is storage in the
hulls and it has a bracket for an outboard. Jessie martin sailed this
boat from brisbane to cape york, and my boat was sailed from sydney to
brisbane. It does well in moderate swell.

In general i'd say its not really worth it buying one of these 'souped
up' 14's... they are pricier and you dont get much more out of them.
Im glad i bought mine, but its very puspose specific I guess. If
you're not going to buy a super cheapy then you need to spend quite a
lot more, like perhaps $2000+ second hand to get something worthwhile.
As you get up into the $2000~$3000 range you get bigger cats, 17,19,21
feet with a lot more flotation, better speed, more sail area, jibs and
sometimes spinnakers as well as better fittings. These bigger cats are
fast fast fast, but in general more difficult to move or park (bigger
trailers, much bigger mast) harder to rig, needing at least two people
and generally you wont want to be out sailing in one of these alone if
the wind is fresh. In general these boats require more commitment, and
i would say they are less forgiving of mistakes. Definitely not
learner material ;-)

A smaller fully battened single sail cat with centreboards if your
sailing in deeper waters, or without if you're in very shallow waters
is an excellent choice for a first cat. You'll get to do a lot of
gybing, not very much tacking, and you'll learn a lot about sailing in
general. Get someone who sails cats to give you some tips on sail
trimming. Just make sure the fittings and hulls are in good condition
even if you have to pay a bit more; the cost of these things can easily
be a lot more than the boat is worth. Trampolines can be re-stitched
for very little money, stays and ropes are fairly cheap and sails can
often be repaired easily if the damage is minor.