Welcome to Beading Daily Forum Amy.
I was using the 10 for $1.00 Bangles from Dollor Tree stores for the inside of the Tubular bracelets.
I have recently started using Old oxygen tubes for my Tubular bracelets.(I dip it in boiling water to sanitize before using)
Hope this gives you some ideas, maybe tubing for fish tanks would be less expensive.
Stop in often and share some of your beading pictures.