The really good gym quality spin bikes are very expensive. These are configurable all kinds of ways, including with triathlon and time trial bike type arm rests with aero bars.

You'd probably be better off trying some spin classes in gyms with good exercise bikes.

An alternative -- one I'm considering myself -- is a CycleOps Fluid trainer. These pop up on craigslist often for under $100, often nearly new because folks get 'em as gifts and lose interest. The manufacturer has a good reputation for customer support.

Add your own bike and you've got a good home spin bike that can be put up quickly and put away when not needed.

I also have a bum back and neck, with permanent C2 damage and frequent neck pain. So I rotate among three very different bikes depending on how my neck feels. I like my road bike for fast rides on smooth pavement, but it's literally a pain in the neck on rough roads. And 30 miles is my limit -- beyond that neck spasms quickly sap all the fun out. But it'd be a perfect bike for a CycleOps type trainer.

My other bikes are hybrids with a more upright ride. Both have quill stems which are easily adjustable for height. If I added an adjustable articulating stem I could also quickly adjust for reach to suit how I felt on any given day.

There are some good fitness/comfort hybrids with adjustable stems and handlebars. Check Trek, Specialized and several others. Or add an articulating stem to any other bike.

Also, some folding bikes from Dahon and many others offer fully adjustable stems. And those can be tucked away in a closet, then pulled out for a ride around the neighborhood or on a bike friendly trail.