The aluminum really varies based on the source. If you go to the local hardware store your looking at a few hundred dollars. I ordered the stuff from
Skagit River Steel and
8020 incs local vender. The rest of the parts came from places like ACE hardware (screws and such, AndyMark (the big 60 tooth sprocket.) All the other stuff came from the kit of parts.
I think the real problem at this point for your team is time. You probably have your base all worked out. Adding an arm with just over a week left will put your team in a pretty tight spot. Consider this. You will either have to go to the local hardware store and pay $7-10 and up per aluminum pole. or, you have to order the stuff which means you lose time to shipping. Then there is the whole trying to get what you make to fit onto your robot...Oh yeah...and the whole programming thing.
You could always use this with the 30 pound withholding limit and get a working arm done between now and your regional, but that puts you in the hard spot of changing strategies at the regional.
Perhaps you would be better off making some way for your robot to be a "runner" where it can get tubes from one side and ferry them to the scoring zone where a ground loader can lift them up and score with them. The rest of the time you can focus on defense and deploying a minibot.
Hope this helps.
Edoga