I agree - I think you can sell it as a pdf.
Pre-buy stuff you'd need on your website:
1. pictures of the completed lure are important.
2. possibly pictures of a couple of stages.
3. possibly a materials list posted before you buy it
(this list would obviously depend on how easy it is to build the lure -- if that's enough to know how to do it, i wouldn't post it all).
And offer a 100%, no questions, money-back guarantee -- it makes me feel more comfortable purchasing things when I know I can return it (since it costs you the same whether you sell 1 or 1000 you don't lose money returning it - but it can help people feel comfortable buying it). The copy is compelling (though the $600 reasoning might be a little over the top). But I would continue to emphasize how easy it is to make, and that once you have the plans you can make extras and gifts! (I thought that was a great idea).
Offering it free might generate adsense revenue - but then again you'd be discouraging clicks on the ads (selling lures). I'd suggest selling it. $9.95 seems like a good price range -- but I'm not an angler... You'd have to ask someone who would buy it (though I was tempted as I have family who fish and they might really like the plans).
You could also get lots of traffic if you post articles or threads in forum and on websites (use your signature line to promote it). If you've got multiple designs, you could give one away free while holding back the superior design (if they are significantly different enough) which would allow people to try one design while purchasing the second (which you could give away on angler sites with links to your other product). For example, maybe a specific type of fishing lure vs. your generic type (or one that i readily available - like a "how-to" article on creating fly-fishing lures).
You can use something like CutePDF to convert a design manual and then allow it to be downloaded after purchase (or emailed after purchase). Using a gateway like PayPal will ensure customer confidence. You can purchase and install simple scripts which will take payment and then allow a purchaser to download the file (only after successful payment). Something like this would cost under $15. I'm sure there are free ones too. But there are plenty of high quality scripts at codecanyon.net (if you have confidence and the ability).
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