onefromzero

For an absolute quantitation you do just once or so and you don't want to bother with cloning, using purified amplicons as standards is a way. You should run them on gel, gel extract, clean up and quantify and then calculate the copy number. It's better to mix it with some dummy nucleic acid, but since you work with PCR product anyway, maybe it doesn't matter. You need to use the standards fresh, they degrade while in storage.

If you intend to use it regulary, invest into TOPO cloning. Ligate your product to selfligating plasmid either TA version or Blunt with killer gene (Invitrogen sells those for example) in 5 minutes and very high efficiency. You can buy kit together with cells. Then you purify plasmid, quantify, calculate copy number  and dilute with E.coli 18S 23S RNA from Roche as a dummy NA and you can have your standard almost forever.

The second biggest problem apart from PCR products degrading from ends is that low complexity templates amplify differently than real template. That's why the dummy RNA is used.