Whilst "best bang for buck" is obviously relative to both the price paid and enjoyment of the fragrance purchased (for me the likes of VCA, Kouros, Rive Gauche, Yatagan are all excellent value, as I would readily pay more than the going rate for these scents, however others may not), in my opinion there are some tremendous scents available at very low prices (less than €10).
Included in these, I would certainly have One Man Show, Everlast, Pierre Cardin, Bowling Green, Cuba Gold, Worth Pour Homme and my most recent discovery (thanks to powerhouse group), Lomani. The latter at at €7 represents (to me) the best bang for buck value I have obtained at retail (Ebay can throw up some great value from time to time).