How long can I legally stay in Dubai as a tourist?

ed in Dubai for 2 contracts so far lasting a year in total. In those 2 my Visa was all done by the employers so I didn't have to do any Visa runs.

In my last month there before the contract was up, I heard about a new 90-day tourist visa coming into play this year and cost about 800 AED

Question

How does this work? Do I pay for it on arrival or go to an embassy when there to get it?

Another Question

Once the 90 days are up can I go to Abu Dhabi to do a run, come back to Dubai and buy another 90 day visa?

Thanks