The Red Sox deal would have never been made had Cherington still been around. Cherington had been in charge of the farm system, and was very reluctant to trade prospects he signed or developed. Dombrowski, his replacement who made the Sale deal, had no such ties with prospects, and readily traded them, especially those not needed near term, for stars needed to fill holes. Sale, by the way, had a very favorable contract--salary about half that of FA sign Price.
Ainge thus far has seemed more like Cherington than Dombrowski--reluctant to trade his draft picks or draftees (= prospects). But he may reconsider this summer during draft time, when he may see FAs as too expensive with the new max salaries in $30M range--relative to Butler's favorable contract at $20M per year. He may be forced to trade rather than to sign a max FA. There is a blog by Smith somewhere here that shows the difficulty Ainge may have freeing enough cap space to sign a maxFA like Hayward. A trade would appear to be an easier route.