We've done this a few times before, but may as well do it again.
Let's say Price is a league average starter and a run better than your league average reliever, and that he theoretically is placed in situations that mirror Grant Balfour's last season. Simply, we'll use Balfour's leverage index and assume Price will be called upon in almost exactly the same scenarios.
That gives us:
~150 innings (assuming he makes ~30 starts, that's five innings per outing) with a 4.48 run average. That's about 17 leveraged runs saved.
~75 innings (half of his starting work) with a ~1.3 leverage and a 3.13 run average. That's 16.4 leveraged runs saved.
So an average starter gives you more value in 150 innings than an above average set-up man does in 75 innings. Of course that's assuming Price is league average as a starter, only goes 5 innings per start, ect., but he's going to have to be extremely good out of the bullpen to match a league average starter's value.