If you're not quite sure what you want, I'd almost be tempted to spend the €20 on 4 different bottles of ~€5 in the nearest moderate sized supermarket. Odds are at least one will be nice, and 2 decent, plus you'll get to experience a bit more variety!

Otherwise, try finding a smallish wine shop, and ask them for advice. A chain one like Nicolas should be fine, I've had some good help from them on moderate priced stuff before.

Oh, and a French-English dictionary may help, while a copy of Lexivin / Lexiwine for the more obscure wine and tasting related words you might find yourself wanting if discussing French wines!