I'd go for the SuperNanny technique. It makes for a long few days (so I'd do it over a weekend if possible), but I think ultimately it's the best and cheapest route to go.
Yes, you can buy gates, door knob covers, a music machine, a new nightlight, cool bedsheets, etc. but ultimately he has to "get it" that he's not going to get anything out of night waking except a march back into his own bed without talking, a drink of water, an extra hug, etc.
I realize it sounds kind of harsh, to keep marching a small child back into their room and bed without any interaction with them. I look at it as my kids get enough hugs and kisses during the daytime, so at night, it's "Good night sweetheart." And that's IT.
Yes, I do practice what I preach. We go through this sometimes after vacations or times when our kids get off their normal routine. We nip it in the bud because we've tried the loving/cuddling approach and every thing else out there in the "sleep books".
I hope you find a solution that works for you. I know being severely sleep deprived is hard on the whole family.