I don't know if its worth getting involved with Drupal for such a simple task. But Drupal has a Classifieds module that is quite flexible. Since it uses the Drupal framework you can give it search engine friendly url's and stuff like that.
However you really need to learn a bit about Drupal to use it. You can also use Drupal's CCK (Content Construction Kit) and Views (An SQL Query Builder) Modules to arrange and sort it by desired fields such as Location, Ad Type, Price etc...
It would be a bit of work though and its not really what Drupal's sole purpose is, but it would be relatively efficient at it.
I've used reefLESS classifieds software.
I found this script in google "Seo friendly classifieds script"
I like it. May be you can find better solution, but i couldn't.
Good luck "blacknight".
I contacted REEFLESS Home page :: Boat classifieds software - flexible, multifunctional, SEO friendly classifieds script , and I would beware of them. It's $600 for the SW, they are located in Russian, but they don't supply proper WHOIS / Phone / Address details. I was not able to get a review of their reefless SW
We had a boat and jetski classified site as like a hobby thing up until recently. We ran it on a windoooz server so seo urls were not an option, however listing regularly popped up number one in google and yahoo relating to the product listed. Have a look at the 68 classifieds website, good software with regular update also using smarty templates.
Maybe but I remember trying this a few years back with iis filters and the results were poor, now search engines do not have a problem with most dynamic urls I just never bothered trying anything new.
I still have the licience for the software so may throw together a site for small ads classifieds