Well to get you started on the right foot, you can get a 20 or 30 foot long PBC pipe from the pluming department at your "Home Depot" or "Osh" for 2$ or so give or take 50 since. this is long enough for you to make a couple of things or mess it up and try again...
Wile there get your self the cheapest duct take you can get per foot. and some electrical tape.
Ok so to start it is PVC you are looking for. As a weapon marshal I would recommend 1/2' schedule 40 for short weapons and 3/4" schedule 40 for longswords. for 2 handers Pvc is not the best option.
personally I prefer kitespar from tap plastics for all lengths of weapons. it is more expensive but worth the few extra buck. currently @ Tap .505 (great for shoter weapons, usually fine for longswords as well) is 8.00 for a 54" piece
.524 (what I personally prefer for longswords) is 9.35 for a 54" piece
. 745 ( good for longs and fantastic for 2 handers) is 15.25 for a 65" piece
I actually would recommend against buying the super cheap tape, it does not stick as well and it is very thin and generally low quality and in the long run not worth the lesser cost.
As for the body of the weapons foam, you can get pool noodles from the "Dollar Tree" for 1$ a pop i suggest getting 2 or 3 to go with your long part of pipe, and for having extra for messing cuts up or making cross bars. note some times you can get electrical tape there too, 2 for a $ nice deal, but that's not allays the case.
Pool noodles are generally lighter then the 3/4 wall foam from almost any hardware store, but like Sarah said they tend to break down and need replacing far far more frequently so on a cost comparison they are in the long run not any cheaper then insulation foam. add to that that the quality of the noodles are very broad I have found some that even though technically meet the size requirement I would not pass as legal due to the compression of them.
I would recommend against pool noodles in general.
for tip foam I again agree with sarah that Joanns fabric is a great place to go I usually get the green stuff which is a double density foam. an old couch is also a good option the key is to use foam that will not compress so much as to be able to feel the end of the foam tube
my advice comes from many years of experience in making them.
Like sarah said we are more then willing to help ya out.