Bruce,
If you're like me and only really want it for fishing alpine lakes and possibly the occasional lake crossing, you may consider the Flyweight Designs Flytepacker and/or CrossFlyte. The Flytepacker has been discontinued since the Crossflyte came out with the intention of replacing it, however he is doing another run of 50 that is due from the manufacturer this week and will be up for sale soon (will be placing an order myself). The Flytepacker is much lighter than the Alpacka's, however as such is isn't really designed for river use. It is significantly wider than most pack rafts and therefore inefficient paddling wise, so not ideal for long treks. The Crossflyte is narrower and supposedly tracks better than the Flytepacker, but not as well as a Alpacka. It is a little tougher because the design is closer to that of a fly fishing tube with a skin wrapped around an inner tube. Again, not sure if it fits what you want, but something you may consider. Also, both are significantly cheaper than an Alpacka.
On a side note, I am currently working on a project for a 3D printed paddle head that will universally attach to the end of most trekking poles (I only say most cause I am making it as big as my thickest pole and can only measure what I or friends have). I doubt that it would stand up to significant stress on a river, but should be good enough for lakes. My goal weight is under 6 oz. I plan on a 4th design iteration soon that may actually make it to the printer so I can get it out and tested. If anyone would be interested or would like to contribute measurements of your thickest trekking poles to ensure that you are covered, feel free to PM me. If this works out, I may eventually design something that could be used for more demanding uses.