I’m looking for a used economy car that gets over 40mpg. I’ve found a Dodge Colt that gets 50+mpg. What else is out there?
Not much. Go to the EPA mpg web site, look around.
I think you mean you found a Dodge Colt that the owner claims gets 50 MPG. Big difference there.
Look for a late 70’s, early 80’s Honda Civic CVCC.
There are only a few cars that get a legitimate 40 or more mpg. Old VW diesel rabbits, used Prius, perhaps used Honda Civic Hybrids, and the original Honda Insight.
If you’re talking in-town driving, 40 mpg will be very difficult except for a Prius. My brother does get about 40 mpg with his 2002 Civic on the highway at 65 mph.
Yes, look at www.fueleconomy.gov . This shows cars going back to model year 1984 with the new revised MPG figures that new cars are rated under. You can also search by MPG for cars newer than 1994. I’ll give you a hint: I was able to very quickly determine that the '94 3-cylinder Geo Metro got 41 MPG (46 for the xfi sub model), but nothing until the 2000 Honda Insight got over 40 combined.
The 1990 Dodge Colt gets 33 MPG with the manual transmission on the highway according to the EPA. The auto trans Colts get 31.
VW Jetta/Golf/Beetle TDI(diesel)
I’d say to look at the Geo Metro. Or, if you need something with a back seat and that has made an attempt at being comfortable, the Prius.
These cars, being in high demand, command premium prices way beyond what they are worth. You will NEVER save enough in fuel costs to make up for the difference.
There was a 4 speed manual and a 5 speed manual that year, the 4 speed got 36 on the highway, and it was faster 0-60
It may be the one I mentioned if your mileage figure is the old EPA method. I just pulled my data from fueleconomy.com, so it’s the new method. If not, it must have been limited production. fueleconomy.com has some obscure cars that I’m not familiar with; mostly alternative fuels in familiar cars.
Pizza delivery people like Geo Metros. Check out a Chevrolet Cobalt XFE but only 37 highway per EPA and you get a manual trans. Otherwise it’s VW TDI diesel, 40ish MPG or an old VW diesel 1992 or older, good for 50 mpg without much effort.
If you insist on 50, get a Harley 883 Sportster and drive it carefully or any brand 500cc max motorcycle.
Find a young couple who own a Miata and just found out they are going to enlarge their family. 
My 1984 VW Jetta, Diesel, gets a legitimate 47 MPG, maybe goes down to 40 in the winter. Runs like a top, have driven it thousands of miles, and cost less than 1500$. One time, with a tail wind, in Alabama, I got a legitimate 62 mpg! couldn’t believe it, thought the gauge had broken! pulled in, filled up, and verified it…
The Ford Festiva is a good disposable economy car. The Festiva is really a KIA. Ford imported them in the late 80’s/early 90’s before KIA was in the US.