If the Rays are seriously pondering trading Carl Crawford within the next month and a half, they have two templates to work from. Two seasons ago the Rangers shipped Mark Teixeira to the Braves for an unholy package - some of those parts are the reason why the Rangers are on their way to the playoffs as of today - and last year the Pirates swapped Jason Bay around in a three-team deal. Both had a season and a half remaining on their deals, and not surprisingly, were close in value to what Crawford is.
Financially Carl is right in between the duo. If a team trades for him right at the halfway point they'll owe Carl about 4 million this season and 10 million next year. Teixeira was owed 4.5 and 12.5; Bay was owed 2.9 and 7.5 million. That's ~14 million, ~17 million, and ~10 million. That's just about the average of Bay/Teixeira.
In terms of playing performance, let's use FanGraphs WAR. Year "n" is the year of being traded to that date, n-1 is the year before, and so on.
Of course, the metrics that some front offices use will vary, but FanGraphs WAR is the best one publicly available and close enough for our purposes. Crawford is right there with the pair.
The Rays owe it to themselves to listen. If someone hits them with a Teixeira-like package, holy crap do it.