No idea about cost for a new top for your car; pretty sure it would have to be custom made due to the rarity of the body style.
You mentioned that it had been sitting in a garage since 1969. You don't say whether it had a cover over the car or not, but if it didn't, I would be pretty sure that quite a bit of airborne dust, pollen, sap, etc. has made its way into the fabric even sitting in a garage. If the overall condition of the fabric looks to be fairly sound, why not think about giving it a good cleaning to help bring back some of the flexibility and resilience of the fabric and remove some 70+ years of embedded dirt? You would need to decide whether it could withstand a gentle cleaning with top cleaner soap, a soft brush, and water. Check out this link to see if you think it would make sense to tackle it.
https://autoforge.net/collections/ra...tible-top-care