I'll preface this review by saying that we planned to do this hike before we came to Atitlan, then were talked out of doing it by hearing stories from other travelers and reviews here, then opted to do the hike after no guides were available for another one. If you're doubting your ability - do it!
We booked through Asotour via our hotel in Santa Cruz and paid $25 per person (about Q200 per person) for a guide, entrance and tuk-tuk transfers to and from. We got to the trailhead around 8:00 AM, and I'd recommend going even earlier if possible to ensure the clouds don't roll in by the afternoon.
We were prepared for a strenuous hike, and its definitely challenging. It combines 5000 ft of climbing (think 3 hrs on a stairmaster at a 60 degree pitch) with high elevation (peak is ~9,000 ft) and we were definitely not adjusted to the elevation so respiration was difficult.
We're in our 20s/30s and I consider myself in good shape (I run 3-5 miles a couple of times a week) but my husband is pretty much the opposite. It took us 3 hours up, 1.5 down and we were both gassed by the end. Our guide said that was a pretty average pace.
We actually brought more water than we needed (3L per person - 2L would have been fine) and you should definitely bring snacks - purchasing by the boat dock is easy. Sunscreen and bug spray is also a good idea, although most of the trail is well-shaded.
The trail itself is fairly well marked - you could probably do it without a guide but you should get one to support the local economy and in case someone gets hurt. But I wouldn't call the trail in excellent condition. Hiking boots would be great especially if the weather is/has been bad, but we did it with running shoes with no problem.