Don't know the monetary cost of that bombing
The cost of the Tomohawks is about $93.31 million (About $1.59 million each times 59 of them.)
As to the greater issue, other than my obvious fulfillment of pointing out hypocrisy wherever I find it, of course I'm not in favor of chemical attacks against civilians.
I am VERY worried about us getting dragged into another quagmire with no clear way out.
Assad is an evil dictator, but one of the main forces fighting against him is ISIS. If we take out Assad, there's a decent chance we just gave ISIS a larger homeland and more resources to build their base and strike out from.
When we attack Assad, we're helping ISIS. When we attack ISIS, we're helping Assad. Is that REALLY a situation we want to be in? (We've literally attacked both sides in this civil war now. On September 23rd 2014 we fired 47 Tomahawks at ISIS targets in Syria)
(Yes, there are other rebel forces fighting against Assad besides ISIS, but they're one of the big ones and would definitely gain a lot if Assad were taken out.)
I just get very worried about us risking WWIII over a situation like this where there really aren't any "good guys" to back.
Read up some on the Syrian Civil War, the whole region is a mess, it's one snake pit after another, but Syria is REALLY messed up, and I don't want to see us wasting American blood for something with no clear way out.
https://en.wikipedia.org/wiki/Syrian_Civil_War(Disclaimer - After I've slept on it, IF we just stick to a few token bombings to remind Assad to not be a COMPLETE dick I'm mostly okay with it, but any escalation beyond that, especially if it involves US personnel being put in harm's way, I'm not so okay with it, and stand behind the stance that it would require congressional approval first.)
And that's of course assuming we have real, good intel that Assad really did use chemical weapons... I mean, according to John Kerry and the obviously unbiased Politifact, he didn't have any chemical weapons to use:

If memory serves correctly, we made a deal with the Russians for them to get the chemical agents out.