Hi Stephen,
I would suggest going for the largest single stack you can get. You can always double stack at a later date.
The double stack does enhance the surface and disc details but the cost is significant as you have found. It reduces the angstrom, the Lunt site goes through this and alot of other factors:
https://luntsolarsystems.com/a-simpl...ar-telescopes/
I had the lunt 60mm and still have the lunt 100mm double stack. I got both my Lunts from Andrews Communication, they were great to deal with.
The larger blocking filter means more space around the sun.
Mel