I am hardly an expert in this area, but I think the discount wines available at Trader Joe's are an excellent bargain! (Some are only a few dollars a bottle).
A less specific suggestion, would be to check out a local winery if there are any in your area. Often local wineries (especially if they are small and/or newer) have very competitive pricing, particularly if you go right to their facility. Going to their facility will also typically provide the opportunity for a tasting, so you can ensure you like the wine before purchasing.