Yep. That's what I would figure too. $10K all in for a nice convertible.Top, interior, brakes and mechanical upgrade ........ about $4K to do it right. You'll still keep your head above water and have a great car.
You could even do it in stages. Buy the car for $5500. Upgrade the mechanicals and drive it. New top next... then interior and other cosmetics.
Good entry level 'vert. I'd do it.