The best deal on multivitamins is frankly the large container of multivitamins at the big discount stores. Get a container that is manufactured by a well known respected company just to be sure.
Chances are the quality will be good, prices are great.
Personally, I buy CVS brand multi-vitamins, 365 in a bottle, normally on 2 for 1 sale. I take one with breakfast, one with dinner. So my purchase is good for a whole year.