Like many things dulcimer, it depends... on what you consider "short" and "inexpensive". Personally I would not touch a First Act dulcimer. We'd had far too many reports here and elsewhere about poor fret spacing and shoddy workmanship making them mostly unplayable. Same thing with the Seagull Merlin stick instruments.
We seldom even think of dulcimer in terms of their overall length. But a 30" overall dulcimer will probably have a VSL of under 24". There are several that fit that size criteria including Dave Lynch's Travel Dulcimer at Sweetwoodsinstruments.com , David Beede's Eedy Beede model, and McSpadden's Ginger. But they are not "inexpensive", with prices from $225 to over $500.
Inexpensive but not short are the cardboard dulcimers, from a couple different makers, with about 27" VSLs and corregated bodies. Overall length perhaps 34". Priced from $75 to $90. They have superior fret spacing so you get good, clean notes, but are basically the same size as conventional dulcimers.
If you have relatively simple woodworking skills you can build a simple box dulcimer with any VSL you want for about $50 in materials -- two sides, two ends, top & bottom, staple frets and autoharp tuning pins. Although technically a zither, not a dulcimer, I am just about to start building one similar to the attached photo. It's going to be 24" overall, 4" wide, and about 1" deep, with a 20-22" VSL. I'm building it specifically to fit in a suitcase for upcoming trips to England and Scotland, where I've been asked to play and there are no available loner dulcimers.