It depends on whether you expect a three-course meal with wine, tax, and tip for under $30, or just the cost of an entree. You can easily find entrees under $30, but not a full meal at a nice restaurant with everything included.
My suggestion is
Campagnola, in Evanston. Finer dining ("white tablecloth") type place, excellent Italian food, moderately priced (entrees around $20), with the romantic atmosphere you're looking for.