We purchased 2-day ticket package that included a river tour at $49 each. The first day we took a Lyft ride to the hop-on starting point next to the Alamo. After touring there we climbed aboard the tour bus to get the lay of the land and see where things were located. We encountered lots of construction detours so buses didn't stop at some of the places indicated on the map. Instead, they stopped as many as 2-3 blocks away and vaguely pointed to where you should walk to see the attraction and where to get the next bus, but we couldn't find signs identifying those temporary stops and they weren't shown on the map. I'm currently using a cane due to a foot/ankle injury and the extra walking contributed to a very exhausting and painful day. Because we couldn't find the hop-on bus stops to get back to the Alamo, we ended up taking a local VIA bus ($1.30 each for one-way ride) back to where we were staying in the Monte Vista neighborhood.
On our second day, we took a VIA bus back downtown ($2.75 each for an unlimited rides day pass) to go to the Riverwalk location specified for our cruise pickup (Casa Rio restaurant). Low and behold, the Riverwalk was blocked off just before the designated pickup point. No advance warning that we would have to access it from a different direction. We had turn around, find a stairway to gain access to the street, cross over the river, walk at least a half mile -- making several more detours due to construction and getting lost -- before crossing back over the river and down more stairs in order to walk back to the pickup point. River cruise was very enjoyable and our guide, Mitch, was knowledgeable and funny. Never did find any of the hop-on stops to go back to the things we wanted to see up at street level.
SA's public transit is excellent and very reasonable. There are buses (VIVA) that drive the centro/downtown sights, the museums and the mission trail. $2.75 for a daily pass allows you to take unlimited rides on ANY route. Do yourself a favor and save money. Find VIA routes online. You won't have a canned audio tour guide (that you can hardly hear over the loud bus engine and traffic) but you should be able to see plenty of great sights during your visit to San Antonio -- for a lot less money!