Gosh, 30 feet is a small space to live aboard...but your $20k budget definitely limits you in terms of finding something larger. You're also going to be looking at boats with serious functional obsolescence and/or major issues with that price. Something that may be perfectly suitable for dockside living, but will require a good towboatus membership to take sailing fairly often.
I dont know who you're speakin to that says Catalina as a brand is unreliable. I think the reliabiilty is more a function of *AGE*...most anything mechanical immersed in seawater for 30 years is going to have reliability issues....try dunking a toyota in the ocean for a few years and see what you get out
One thing to remember...other than the fiberglass layup, very little on a boat is really made by the manufacturer...its all parts/components from various vendors...and the reliability of those parts is very much on the owner who has changed, swapped out, upgraded, fixed, or jury rigged various components over 30 years of boat ownership.
Cape Dory's are very sturdy, bluewater boats...pretty much the opposite of the Catalina in terms of purpose of the design. For what your intent is (learning to sail, coastal sailing, no offshore passagemaking) it may be too spartan in terms of creature comforts and space.
Now, if your intent is to take your boat offshore or do some serious ocean passagemaking (Hawaii, Fiji, crossing oceans outside of a weather forecast window) then the Cape Dory would be the boat I'd prefer.