What brand/model of DSM are you planning to use on the frame? The carriages for a short arm vs longarm would be different.
I have a midarm machine (Voyager 17) on a Hinterberg stretch frame. This is a great beginner frame if you have a shortarm because you can use a shortarm on it and then, if you upgrade to a midarm such as the Voyager, you don't have to change the frame. This frame is wood.
Ideally you want to buy a longarm together with its frame at the same time, as many high-end machines are made to work with a specific frame.
If you or your husband is handy with tools and wood, you might want to make your own frame to save money. There are directions and parts on eBay for a freestanding frame (and carriages available for both shortarm and longarm). Also, there is a relatively inexpensive table frame kit available (about $250 for the kit, I think).
I can post links for the frame kits if you are interested.