There are two places to haggle for lobster: the front end and the back end. The back end is obvious -- if you can find lobster nearing its expiration, you've found a ripe deal (no pun intended). Spoiled shellfish isn't worth its space in a dumpster, so feel free to offer a rock bottom price.
That said, if shellfish of questionable freshness isn't your thing, consider going to the front end. The Maine newspaper "Working Waterfront" describes the markup on lobster, from the first buyer at the dock, to the trucker who transports it, to a large wholesaler who grades it, to a small wholesaler who sells to markets, and finally, to markets that mark it up to the price you see on shelves. Each step adds to the cost.
If you can't walk onto a dock and offer to buy your lobster straight off the boat, try going online to get as close to the dock as possible. When searching for a seller, include "coop" in your search terms, which will lead you to fishermen cooperatives that sell direct from the boat. If you can figure out how many steps removed the company is from a lobster pot, you can figure out how much to offer.
But even a break-even price on lobster is dependent on finding someone willing to pay it. Lobster is a luxury item, and in tough economic times, people simply don't buy. So anywhere in the markup chain, you may find desperate sellers looking to unload lobster at any price, even if it means selling for a loss.