I would like to clear a few things up.

1. It is not 2 months of Cliff Lee. It would be 3 months for the rest of the season. But it's really 4 months as they are aiming for the playoffs (anyone aquiring him).
2. Poll the GM's. They would prefer 2 months of Cliff Lee over a year. They only pay a portion of the salary. More importantly they only pay the salary and give up prospects if they are 100% in the playoff chase.
3. When talking value of Star A (in shortened time frame) versus Prospect B (with full control) it's best to evaluate fairly. Cliff Lee will help Texas (or other org) for 2010 only. It's not 2 months it's one year. But it's certainly not 5 years either. But let's look deeper:

• Texas only makes the playoffs every 5 years or so (ok I'm lazy to look it up and I know it's less often). Cliff Lee or Star A would help them in that one year they are in the playoffs. Prospect B will be there for 5 years but we can only expect one year in which he helps a playoff team. Yeah, with Texas I expect/hope this will become more frequent but we can't count on it.
• Most of a prospects value hinges on their low cost to the team. If they are high cost then a free agent can replace them easily. Prospect B thus has more "apparent" value when he develops slowly. Of course he then gives only a small amount of value to the team then. If he has a meteoric rise then 2-3 years in he will be paid like a free agent (less the years commitment). This negates the value over the Star A as the prospect is now paid like a free agent.
• Value of the prospect. Many mention the 2-4 million paid to the prospect. That is sunk cost just like the sunk costs from the other side of the trade.
• Value of compensatory picks. They usually don't equate the same value as what came over in the trade. Not important. If the Twins trade Ramos and Hicks for Lee it's really Ramos + Hicks for Lee + picks. That doesn't sound as sexy to me.
• Purpose. It's not to make the playoffs. Or to compete. It's to win the World Series. All fans expect their teams to take the shot when they have the chance. As it stands Minnesota & Texas have almost no chance of making the World Series. The addition of Lee makes them a World Series contender.
• Comparing to CC. When CC was on the market he had poor playoff series. He also had a poor ERA for Cleveland in an excellent pitchers park. And he is fat. Many questions. It wasn't until after the trade to Milwaukee that he answered all the questions. He was unbelievable. And thus the NY contract.
• C. Lee. A few years ago he might have went for less. He was an enigma. But after pitching with serious injuries for a year or two he really emerged. He backed up a dominant season with another. He was traded to another league, to a pitching park, to a competitor. And he excelled. Then in the playoffs he took another step. Then in Seattle he has taken another forward. Why would he get more? It's pretty obvious to me.