Do you have numbers behind that for relative comparison? It's far cheaper to build a great bullpen than a great SP rotation or a great offense. If a great bullpen is as valuable, or nearly as valuable as a great SP rotation or a great offense, then why does this club (and this board) continuously puts the BP at such low priority?
Blue Jays hitters WPA last year (min 10 plate appearances to remove pitchers from interleague play) was 10.99. If you want to count all at bats it drops to 10.72 which lead the league.
Last year the Pirates had the best BP WPA at 11.80. By comparison the Jays were 27th at -1.81.
For starters the Cardinals topped the league at 14.09. Jays were 18th at 1.28.
Based on this, my intuition was somewhat right. All 3 probably hold close to equal value -- if you are elite in 1 area you have a shot. The Jays had close to average SP, a terrible BP and the best offense and they made it to the ALCS, losing to the eventual WS Champs in a 6 game series. You don't need to be elite everywhere. Being even average in 2 of these areas, and near the top in another and you're in good shape, and then it comes down to whether you get hot at the right time, don't get cold at the wrong time (which happened to the Jays against the Royals) and the baseball gods. People saying the Jays need to add 2 more pen arms, or another starter simply want the world, but it's certainly not required to be above average everywhere. That's incredibly hard to build - a lot has to go right.
Also of interest, in the last 10 years only 3 teams have had BPs with WPAs above 10.00 and 10 times over 9.00. As for offense, over the last 10 years it's happened 6 times over 10.00 and 12 times over 9.00. For Starters it's happened 17 times over 10.00, and 30 times over 9.00.
This doesn't surprise me, as of the 3 groups the relievers get the least amount of playing time (most starters get 2-3x the innings of a reliever), and with WPA being a cumulative stat this means fewer opportunities to add to that win probability. This is probably why the bullpen comes after offense and SP for many teams -- they simply don't get as much playing time and teams on a budget would rather spend on guys that are going to get the most time.
Is building an elite BP cheaper than an offense or rotation? Probably, but it seems to be a lot harder. Here's a link to 2014s top paid relievers;
http://www.sbnation.com/mlb/2014/9/17/6264159/highest-paid-relievers-baseball
A lot of high paid relievers not really doing much, so GMs and Scouts have to search for those needles in a haystack, and be effective for more than a couple years, or find reclamation projects and take a chance on them.
The other thing is bullpens are volatile, have a high turnover rate and are built short term. Relievers don't get 6+ year deals because there's about a 100% chance of that deal going sour and fast. Teams are constantly making moves to their pens. Position players and Starters get those long term deals because they are the best of the best, and are going to be worth the contract for a good chunk of it before they are overpaid in the final years - which is simply the cost of doing business with elite SP/position players thru FA.
