Take a look at the Incra Miter Express for a comparison of these type sleds. I saw the Incra on Ebay at $119 + $20 shipping. I don't have either but I do have two Incra tools (V-27 miter gauge and LS 24 positioner) and both are great quality tools.
I have one. I used it in a woodworking school class and liked it. Then I saw it being sold by the maker at a local show. I think I paid $149, so this is a good price.
Sure you can make one yourself. Yes it is expensive. The equivalent Incra with the sled is more $$.
I found it worthwhile for me, as I did not want to focus my energies on making jigs.
So my choice was easy. This is well made and quite uuseful IMHO.
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