Goldman Sachs (NYSE:GS) is buying Ebix (NASDAQ:EBIX).

That's the long and the short of today's news that Atlanta-based insurance software provider Ebix has agreed to a $20-per-share buyout offer from the investment banker. Including assumed debt, the parties value this transaction at $820 million, and say it represents a tidy 18% premium to Ebix's recent pre-merger-announcement prices.

On the other hand, the price is only about a 7.5% premium over what Ebix shares fetched at close of trading Tuesday, and Ebix shareholders -- and their lawyers -- aren't so sure the buyout price is a good one. The price is also more than 10% below Ebix's valuation a year ago. Shareholder derivative lawsuit announcements challenging the sale are already flying.

Combined with the merger deal's "go-shop" provision, which permits Ebix to seek out better bids from third parties over the next 45 days, investors appear to be betting that Goldman will either have to raise its bid, or see it beat by another bidder.

How do we know this? Ebix shares today rose 10.7% to close at $20.60 -- $0.60 more than Goldman has offered to pay.