plexiglass is very expensive.
I was thinking - - since you do not want to cut into any of the bandanna designs, why not add strips to the smaller blocks to help them match the bigger size?
As far as template, if you are not going to go buy a ruler,
templates can be made out of cereal boxes, soda cracker boxes, any type of cardboard (and you draw around them)
freezer paper ... cheap, cut the size you want, using the technique mentioned above, iron to the back of the fabric and cut out ...
best all round template would be a 6 x 24 inch Omnigrid plastic ruler at your quilt store or local craft store ...
cheaper than plexiglass.
The next ruler I would purchase would be the 6 x 12 plastic ruler ...
and the rotary cutter, and the mat ...
those three/four items will pay for themselves faster than you can make one quilt.