How Much Money Will the Dems Spend in the Primary

Is it plausible that they could agree to limit the amount of money they spend, and then pool their funds for the general election?

Money given to a candidate is money given to a specific candidate. If the candidate fails to pass the primary, campaign finance law allows the candidate to either A) return the money to the donors, B) turn the money over to a registered 501(3)(c) organization (ie a non-profit which may not in any way engage in political discourse) or C) pass the money over to the state and/or national party. If a candidate takes option C, the party may use the money ONLY for "party building" and may NOT use it to directly support an election or candidate.

The reason for these restrictions is very simple: to prevent an end-run around state and federal campaign contribution limits.