I stayed out of the current conversation but finally had to add my two cents.
______________________________________________________________________
I'm the guy that designed and produces the Odd'l Rocket Adeptors. I also write the modelrocketbuilding.blogspot.com blog.
I watch the prices of rocket kits and engines. If I see something I feel is unreasonable, I simply pass up the purchase. It's always your choice.
I sell kits and accessories to vendors at a wholesale cost. While I have a suggested retail price, the vendor sets a final price to make a profit.
The amount of time it takes to make an Adeptor is more than you'd think. I am very picky about quality and fit.
To produce this product, investments included a vise, drill press, metal drills, metal taps, tap handle and fine files Most kitchen table builders probably wouldn't have these tools at hand.
So far, this doesn't include the price of the Adeptor materials and my time. I didn't buy the parts at Home Depot, they don't carry what I require. Who knows? I may have missed them in the fastener aisle. I have bought the large washers at Home Depot.
To Ez2cDave, the product you showed from Lowe's is not what I use. It may have a hole in the side, but it isn't tapped for the thumb screw. That nut may not fit the bolt on a camera tripod.
You'd still need the vise, drills, tap and handle. If you have the tools, time and skills, have at it. But don't forget where you got the inspiration. I give full credit to that picture from the Enerjet News, January 1973.
I'm fortunate to produce (draw, typeset and print) my own instructions. If I had to pay an outside
graphic artist to draw up instructions the retail price might be a little higher.
Add to that, I usually have to pay postage to get the products to vendors.
There is more to small scale product production than the average hobby consumer realizes.
After you've sold a few thousand kits you understand and look differently at domestically produced, small vendor pricing. Where Estes may produce thousands of a single kit design, I produce 25 kits at one time.When you buy in bulk (thousands) and bag kits overseas your wholesale price will be much lower.
The first time I used the prototype Adeptor for a camera tripod launch it saved my sore knees and enhanced my rocketry experience. If I was not the producer, I'd buy one myself.