Inexpensive water resistant cases for boating?

Well, it's always hard choice. I'm also a kayaker and had similar problems. There are 3 solutions generally (excluding mobile phone cameras):

1) dedicated waterproof/underwater camera = compact

2) waterproof case/bag for compact/mirroless/DSLR

3) waterproof storage box/bag onboard

I've tried personally 1) and 2) in reverese order. 3) is quite convinient, as You operate Your camera normally, just hiding it for safety after use. Some risk of flooding equipment is still here, but many people uses their precious DSLRs on kayak trips this way. Definitely not recommended for white water or so. But maybe excellent on bigger boats (sailing?).

2) The most compact and failure free solution is a hard case. But they are very expensive and not universal in the sense they usually fit one particular camera model and nothing else. More affordable are soft camera bags of the type You have linked from Amazon. They can be tricky though. First, they are bulky, holding camera is difficult, also operating controls and zoom (in system cameras). Not all of them have a trully reliable closing. Long time ago I used Eva-Marine for my first digital compact and it was almost O.K. but the stupid small inflating valve, that tended to open spontanously.  Equipment was very bulky in this bag, problematic on a small boat (sometimes I used very small inflatable kayak).

1) This solution I've chosen when I switched to mirrorless from compact as my main photo equipment. Waterproof bag for it would be too bulky to my taste and I didn't want to risk on water quite expensive camera. So currently for water trips I have old Panasonic FT4 (waterproof). Quality of the pictures is much worse than from my mft cameras (E-PL1, E-M10II), but probably not worse than from expensive smartphone models. Other problems is the lack of zoom to photograph effectively birds on water from usual distance. Usually these "tough" compacts have no more than 4-5x zoom. But camera is 100% safe on water, doesn't occupy too much space and is always ready to use. Note, there are currently better underwater compacts that You can use for boating. I would look for Oly TG series. Some models here can even accept dedicated front teleconverter, increasing tele - zoom range significantly. This would be definitely of value for a boater.

Btw, these soft bags from Aquapac in Amazon You've linked look quite well. They definitely improved closing. Many years ago  a I saw similar models of that brand, but closed with Velcro, pure recipe for disaster... So if You accept some inconvinience of bulky bag it can be quite good or perfect solution for You. Especially if  You're not limited to extremaly small inflatable boat You have to sometimes carry by yourself with the rest of the stuff. Just chek the bag before use if it is really fail proof.

In the end, yet another general opinion: on a small boat, that can always capsize in some circumstances, any protecting cover for camera or camera itself, or camera storage have to be 100% waterproof, fully submersible. Otherways, You don't need to protect your camera at all. Binary situation: it wil be O.K. or die just depending on the boat's fate (capsizing) or dropping it overboard. So no raincovers or so...

Regards,

-J.