Hello,
I had a 30 year old cabrio before, now my daily is a 21 year old cabrio. My girlfriend bought for her 1st car a 17 years old cabrio last autumn. Such amount of money is definitely the cost of replacing the whole roof. I don't believe it cannot be repaired at lower cost.
Looking at the 500c photos it has the same type of the roof as my and my girlfriend's daily. It is not a lifted roof as in the bigger cabrios, it just slides down and up on the side rails.
We had to dismantle my girlfriend's roof to give it a thorough clean. Basing on some youtube videos and tutorials it took me around 40 minutes to dismount it and mount it again. Of course I'm not calculating the cleaning time. I needed only some basic tools to take off the plastic covers
On the bottom of the forum banner you've got the link to
ePER. It's a spare parts catalogue. Use you VIN to find the appropriate part numbers and check with a FIAT dealer or on the internet if they are available. When dismantling you'll be able to check what is broken and needs replacement.
From my experiance the weakest points are what FIAT calls Vessels (number 6 in this diagram):
Also the cables (number 5 on this diagram) could need replacement:
First of all, beware as I took the first 500C from the top of the list, as you have not mentionned which year / model your car is. Check with your VIN to have the correct part numbers and diagrams. You can follow the sub-sections you can see on the diagrams to get to the ones you need (except the model of course!).
Then, don't order anything - check the availability of the parts and then during the dismantling process check what parts need replacement and place the order.
Check also what is the required maintenance the roof system needs once you'll have it fixed and take good care of the roof after it will be fixed. The fabric roofs need regular impregnation (I'm doing it twice a year, after and before the winter). I'm using a product called Fabsil Gold Universal Protector
(I was using a spray version until now, but starting this year I'll use the fluid one and a brush, it is more efficient). It's a silicone based fluid, but can be local. For cleaning and colorisation I used British Renovo products and I'm very pleased with them: