Wedding Free Bar price at Cas Mila in ibiza

Hi, I'm planning my wedding for next year at Cas Mila in ibiza. We would like our guests to have a free bar for the evening but the prices per person per hour seems to be quite on the pricey side. It has been suggested that we can leave money behind the bar like a tab. Which I think this will be the option, however, as the price per person per hour is quite expensive. I'm now concern that we may end up spending more if we left a tab. Has anyone recently book here and can offer me the best option? Greatly appreciated and thank you in advance x