all kidding aside - what do you get with a $30 or $50 bottle of merlot, that you don't get for $5.99 at Walmart?
drunker faster? better taste?
imo you don't need a $30 or $50 bottle of merlot. CLos du Bois is very decent at ~12.00 and Murphy Goode has a decent one for ~14.00. Simi is even better at ~18.00 but if you are happy w/ the 5.99 stuff my advice is don't try the others.
Cab is another story. Although you can find really good cab for ~15 imo, some of the higher priced stuff isn't worth it but some is outstanding.