Last week, the EU announced its intent to launch an expanded probe into Google’s (NSDQ: GOOG) acquisition of DoubleClick, prompting real concern that the deal may end up blocked. While the EU’s decision does not prejudge the outcome, it’s always good to have a backup plan. A new research report form Bernstein’s Jeff Lindsay looks at some of the options available to Google, should the EU (or the FTC for that matter) ultimately come down against the acquisition. He lays out four scenarios: a) Forgo competing in the ad-exchange business. b) Purchase another player, possibly ValueClick. C) Build an in-house ad exchange. D) Form a JV, possibly with DoubleClick.

Of these, Lindsay thinks an in-house build is the best option, and he lays out some of the details of what this would entail:

-- Total capex requirement to get a system up and running would be around $250 million, which is based on estimated capex at other companies. DoubleClick, for example, is estimated to have spent $61 million annually in the 2002-2006. aQuantive’s spending was in the same ballpark, at $64 million, while ValueClick’s (NSDQ: VCLK) was a bit less, at $29 million, although it’s growth has been slower.

-- Lindsay estimates that the company could have such a system built and populated with advertisers within two years, based on the rapid growth in the area and the depth of Google’s engineering talent. By of comparison, Right Media got to its level within three years of launch. While two years sounds like a long time, the company would have to expect another long regulatory wait if it were to buy another player, potentially making this option more attractive.

-- The toughest part may be justifying a brand new player in this industry, though Lindsay believes that if it were to steal some market share while expanding the overall pie, it could be justified.

Undoubtedly Eric, Larry and Sergey have already run the numbers on this option and all the others, although the hope is that it all proves academic.

• Updated: EU to Expand Probe into GoogleClick: Report