Right you are about no flight on Saturday... bad luck but the ex-AEP service operates Su M Tu W Th F ...

I think it will be hard to beat the revised quote(s) you've just gotten.

The company my companion here uses is Quickcar... http://www.quickcar.com.ar no idea on pricing, and although their website shows lots of pictures of Mercedes their fleet is mostly Toyota and Citroen sedans from my experience. Quite decent service. I don't know about pricing because he has an account with them. We use them mostly for transfers to and from EZE or AEP as we keep a home here in Capital Federal.

Nevertheless, a quote request to them might not be a bad idea.