That is kind of the thing.
Getting the image is trivial. The real effort is getting it printed and getting a frame for it. And the cost of that tends to be pretty close to just buying a pre-print. And stuff like this tends to be sold in museums or other local/government buildings and genuinely goes towards some great community programs.
That said, there are some great sites for this. There are cheaper websites, but Stackhouse is generally a great choice for printing. Especially if ou want a canvas print. Frames you are almost always best off going to a pawn shop or local art supply store, but even amazon is not a bad choice for that.
Combine that with realizing just how many museums upload high quality scans of genuine works of art and...