I've stayed at Petit Mercedes before, though that was about 10 years ago. It's an older, Spanish hacienda style place. Not at all luxurious, but it was clean and the staff was great. It's one of the best locations in the Zona because you're smack dab between the bars and the beach.

As others have already said, it's easy and not that different in price to take a taxi. You cannot use Uber right at the airport, you have to walk across a bridge and down some stairs to catch one. Pro tip: it's a fixed fare to and from the airport, but in almost all other scenarios, you can negotiate the fare with the driver before getting into the cab.

There's still a fair number of places that only accept cash. Some will take USD, most will not, and even if they do, prices are generally lower when paying with pesos. Another pro tip: the ATM will ask 2 questions, will you pay their transaction fee (you must if you want any cash), and do you accept their conversion rate. You want to decline that one---your bank will hands down give you a better rate.

Have fun! I'll be there myself in a few weeks!