I-394 was about $450 million, but it was several different projects. To date, Crosstown is the single biggest contract in state history. This would change with the Stillwater bridge, assuming it goes as a design-build as I've heard is going to be the case (but don't quote me on that).
Just for the hell of it, I went to MnDOT's EDMS site and downloaded all the I-394 contracts I had not previously downloaded as part of my long-term project to assemble a collection of pattern-accurate MnDOT sign panel detail sheets (for which, by the way, my page count is now in excess of 8,000).
If I exclude all contracts from before about 1980 and from after about 1995, all bridges-only contracts, and all contracts which have a SP number from CS 2789 but have a lead SP number from a lower CS (generally ones corresponding to US 12 between downtown and I-494 and also for intersecting routes like TH 100), then that leaves 35 contracts. This does not include the signing contracts, which I had hoovered up several years ago--for I-394 primary construction there were at least four.
Contract value records based on nominal dollars tend not to be very meaningful because of inflation; it is comparable to the finding that the top ten grossing films of all time were all made in the last twenty years. However, I believe the Crosstown Commons contract is safe from challenge by any older contracts because it was advertised several years after MnDOT switched to turnkey contracts around 2000. Previously it had been MnDOT's practice to advertise large numbers of smaller contracts for grading and drainage, surfacing, bridges, and installation of traffic appliances such as electric lights, signs, signals, guardrail, and TMS. As with I-394, this typically results in literally dozens of individual contracts, none of which will challenge any contract-value records in either real or nominal terms.
BTW, the TH 212 freeway was built (if memory serves) through a single design-build contract which divided the road into multiple sections (some sections corresponding to contiguous lengths of the finished road, and other sections corresponding to work entirely within certain functional disciplines which covered the entire facility--for instance, signing was handled as its own section). The overall contract value was about $240 million.