Woodworking is one of my hobbies....and it's kind of expensive (i'm sure you would agree) ..So i'm always on a budget...
I make my own canvas frames...so obviously i need miter clamps ...and lots of it...here is what i came up with.
Btw...i'v entered this in the woodworking contest...so if you like it and find it useful please rate it and vote for me
thanks.

Step 1: Things You Need

Square dowels...scraps will do
scrap 1/8" mdf ...square...rectangle...doesn't matter
plastic sheet...this too could be scrap...you get it from toy boxes or gift boxes
wood glue
a square ruler.

Step 2: Assenbly

get your scrap mdf and cut it into 2" squares...you needn't be perfect...as you can see my samples :-)
place your square on the mdf and glue 2 square dowels on either side...as in the picture...don't go to the top as you need to leave space for the glue to squeeze out.
now once dry just stapler the dowels or nail them...just to reenforce. place plastic squares in the center so that your work piece will not get stuck to the mdf.
Now sand the top corners so it's slightly rounded.
your miter clamps are done...
now you just need to get an old t-shirt ...start cutting from the bottom at an angle so you can cut along strip going right round the t-shirt.
Attach it to a string lock and then you have your band clamp!

Isn't that like the easiest and cheapest Band miter clamps???