Since we were discussing this earlier I thought I would put some work in on this.  There is a messy, quick example within the Bartlett Declining Defense thread.  The first step is seeing how much value Bartlett carries beyond his contract.  Because Bartlett is an arb-eligible player for 2 more seasons he will be guaranteed to be paid less than the value he is capable of contributing.  Luckily, BTB developed a great Trade Value Calculator.  That link will take you through the whole article that I will be applying to Bartlett.  SO CHECK IT OUT.  On with the pretty pictures:

Basically, if Jason Bartlett can be a 3.05 player over his last 2 years of arbitration he will be worth an extra $11,000,000 to the organization that obtains him.  This is due to out-playing his relatively paltry contract and the $2.5M that his type-B status should be worth in a draft pick. 

OK, so now we know that Bartlett is worth $11M to some interested organization.  "So what?", he says.  Well the next step is to see what that $11M is worth at the prospect level.  Luckily Victor Wang gave us a good idea HERE.  I will reproduce here to make it a little easier to see:

Top 10 hitting prospects	$36.5M
Top 11-25 hitters	$25.1
Top 26-50 hitters	$23.4
Top 51-75 hitters	$14.2
Top 76-100 hitters	$12.5
Top 10 pitching prospects	$15.2
Top 11-25 pitchers	$15.9
Top 26-50 pitchers	$15.9
Top 51-75 pitchers	$12.1
Top 76-100 pitchers	$9.8
Grade B pitchers (as graded by Sickels)	$7.3
Grade B hitters	$5.5
Grade C pitchers 22 or younger	$2.1
Grade C pitchers 23 or older	$1.5
Grade C hitters 22 or younger	$0.7
Grade C hitters 23 or older	$0.5

So we can pick and choose some different options here.  2 Grade B hitters works out nicely.  Feel free to theorize your own possibilities.  So now we need to look at some grades to get an idea of who would be a target.  It's hard to find non-Sickel's draft grades on an ABC scale (if someone can point me in the right direction it would be much obliged) so I will list Sickel's B & B- hitters by team.  Sickels runs a site called Minor League Ball.  A search got me to THIS page.  All of these are from over the winter and were preliminary at the time.  I thought this was good, because if we trade Barty in the offseason there will be a similar list and this gives us an idea of how some of these guys have panned out.  I would have included the positions, but I didn't think to do it until I was half way through and this is already taking up too much of my time.  Here's the list:

Some of these names may be familiar to you and a lot probably won't.  Most of these guys won't ever even be average Major Leaguers, but the point is to find comparable value and then work from there.  This is what I've got for now, but we should revisit it sometime in the offseason and definitely when next years prospect list comes out.