You could also try Code Canyon but php jabbers has been recommended by a few people here, I believe the php jabbers can be dropped into an existing RW page via an HTML stack.
I looked for a similar solution for a garage website for a car sales listing within RW but nothing suited because I was looking for the option to select make then model, plus it had to be usable by external users who didn’t have RW. In the end I bought a script from Code Canyon which was good but is now falling behind in terms of SEO, structured data, sitemap generation. The dev for that has been talking about a newer version for well over a year now, so also looking for a new solution.
I have been considering the php jabbers script but also now looking to see if I can bend TCMS into something that will achieve most of what I want. There are usually only a small number of cars, less than 15, so maybe I don’t need to be too hung up on too many options.
If you’ve found a good solution in php jabbers it might well be worth a go, especially if you get the developer license, so you can edit things as needed. It depends how complex/simple you need the Classified Ads to be, a custom script specifically built for that purpose may well be better in functionality and time saved.
Will be interested to see which solution works