Cheap 6" tube is available from your local nome builders store. Ask for concrete form tubes. If you go to someplace like HomeClub the length may be just what you need while the real construction supply may have them in 20' lengths. This tube is a spiral wound cardbord of fair thickness and you do need to paint it to insure that it doesn't melt from the dew. Flat black inside and something pleasant outside (a starfield is always popular). When you do the assembly, start with the longer tube and put the secondary stuff on first and then put the primary mirror in at a nice focus position. I suggest that you use the shorted FL EP that you can get (4mm is always nice) and set it near the bottom of the focuser's travel. Hopefully, all of the other EPs will be further out and the longest won't want to be too far out - I use the Celestron 40mm (useless EP otherwise) as the far end and is usually set as just beyond the end of travel of the focuser tube.
Have fun! BTW, if you have somebody that has a lathe and mill, you can get them to make you a nice Crayford focuser for very cheap! Go look on the web for the various versions of the design. I have also seen Crayfords built without the need for the above by using wood for the frame to hold the bearings and an undersink trap part for the tube.