Not easily adjustable but fairly light, quite strong, and quite cheap (you could probably somewhat easily design something to make them semi-adjustable), are pre dried/treated bamboo poles. After reading some posts here and seeing some youtube videos, i was inspired to make some. They are not finished, but it looks promising since two 6 foot poles together weigh in at 16 oz. Obviously i will make them much shorter (i expect the finished pair to be somewhere inbetween 9 to 12 or so oz). So far, cost of materials is 6 dollars (bought at Lowes for 2.98 per pole). I plan to add some foam grips, and some rubber stops or pegs on the bottom.
I'm guessing though, you might want or need more fully adjustable poles for your tarp-tent setup. For semi adjustable poles: If you cut one of the poles into two pieces (not cleanly in half though) and add a female to male screw or coupling, or peg in for that one, and a connector on the non cut pole and made the non cut pole slightly longer to compensate for the slight weight difference between the two, it might give you just enough flexibility for use with the tarp tent, but i'm completely speculating and i would probably first ask more experienced people than myself about the feasibility of that. It might be that this could ruin the structural integrity or strength of the one bamboo pole though.
Either way, best of luck.