Richard,
If you have soundfonts then
FlStudio is a good place to look.
There are many versions but the interesting part, for you, is that one can use the demo, full program with some limitations ie save a project, indefinitely. I did so for a year (!) and bought the Producer edition, when my finances settled out and now have free updates for life!!
You can overcome the save by exporting each track as a wav, a bit of a limitation but it works.
It runs as a VSTi OR via rewire.
Also has good proprietary effects and instruments
I find it excellent and use it in every song I produce with BIAB although I haven't tried it as a vsti in BIAB.
try it, it's free and the demo shows how good this program is.
Alyn