http://www.baseballprospectus.com/compensation/cots/national-league-central/chicago-cubs/
Note though that they have Jackson incorrect on here because he was given an $8 signing bonus the first year of the deal making the remaining years $11 mil. They've averaged his deal over the length of the contract.
Your 2013 figures aren't accurate.
Between, Castro, Jackson, Rizzo, Soler, buyouts of Veras and Fujikawa, Conception, and Sweeney they have ~$30 mil committed toward 2015. If you figure arbitration on Castillo, Arrieta and Wood you're probably taking upwards of $15 mil. As for the rest of the arbitration eligible players many are non-tender/trade candidates. You still will need to replace them on the 40 man roster however and they are likely around $15 mil. That gets you to the $60 mil I mentioned.
As for what they spent in 2012/13, the numbers are laid out right there in the link. My math is right.
Additionally, in reference to Tanaka, the cubs reportedly offered him a 6 year $120 mil deal plus the $20 mil posting fee. They could pay the fee over multiple years or all at once but if you assume 6 years $140 that's $23.33 mil. They gave Hammel $6 mil. $23.33 - $6 mil = $17.33. $17.33 + $ 92,677,368 = $110 mil. 2013 was $106,837,810. 2012 was $109,316,000