Glassdoor shows that Mexican software engineers with 1-3 years of experience may get $3,200 a month on average. Central European devs with similar experience make around $3,600 a month. However, you should remember about the taxes and additional fees you may need to pay to the Mexican side.
So, both options are quite affordable, although the final number depends on the duration of the contract, the level of developers, the number of people you need, and the company you hire.