We got lots of quotes and ended up using a 55 pink Caddy convertible for an hour in and around Varadero for 20CUC total for the 4 of us, 25 CUC for the 59 Olds convertible back and 5 CUC for the horse and buggy around town. Priceless.
As Beansntoast says, these aren't real convertibles but topless cars. Original? Absolutely not! With gas at 2CUC/l and diesel around 0.50CUC/l our first ride had a transplanted Mercedes engine, our 2nd, a Mitsubishi and one along the way had a Russian Hino diesel with a Toyota AC unit.
I got some shots of under the hood and though very clean, it's Franken-Car heaven. 10 years ago they had Lada engines.
The horse was 100% organic.
For a trip to Havana, there are newer AC'd vans with great views and comfortable seats. We had quotes as low as 130CUC for 4, return, for a 7 hour day. Also had quotes for 300+CUC for the same trip.