I think Mesko is the superior punter right now, but economics are certainly the deciding factor here. Mesko was slated to earn $1.323m this year. But that is not the real issue. Based on the most recent two punters to sign new deals, the average price for a top punter (and I believe Mesko qualifies) is a little under $4m a year. No way the Pats would shell out anything near that, and I wouldn't blame Mesko for looking for it.
By comparison, here are the salaries for Ryan Allen:
Ryan Allen:
2013 - $405,000
2014 - $495,000
2015 - $585,000
2016 - (RFA Tender?)
In summary, the Pats probably felt that a two-time Ray Guy Award winner at UDFA money for three years is a viable risk/reward given that Mesko would probably walk next year. Sure, it is a gamble but the kind of gamble that BB takes to keep he team on top for so long.