I made a few size 6 bamboo knitting needles out of 12 in. bamboo skewers and a few beads. The skewers cost me $1.99 for 100 of them. The beads I had on hand, but you could pick up a bag of beads for about $2.99. One set of 12 in. bamboo knitting needles would cost you anywhere from $5.75 to $8 or $9. Custom knitting needles can cost you anywhere from $10 to $20.
The only other thing you need is fine grit sandpaper to smooth out the points and some of the rough spots on the bamboo.
The first step is to pick out to skewers that are nice and straight and are the same length.
Next, smooth out the points and the rough edges with your sandpaper.
Then pick out two beads that have a wide enough hole to fit at the end of the skewer. If it's a tight fit you can get away with just twisting the beads on, but if there is a bit more room then clue the beads on with craft clue or E600.
Wait for your glue to dry and then, tada! you have custom knitting needles!
If you want different sizes or different types of wood then you can always use wooden dowels. You would just need to create a point using a standard run of the mill pencil sharpener. You can customize them further with paints or wood stain just make sure to pick a paint or a stain that isn't going to come off onto your hands or your project.