EDIT Nah no cheap parts
Thanks for the suggestion though
You're half right I guess. I'd never go for a full custom system when the likes of Powervalve and Milltek spend literally years developing their systems. In fact Nige told me the R32 style mk5 system was three years in development. In all likelihood any custom exhaust is pretty much a prototype. There will be flaws, it won't be optimised for performance and sound levels, and you can't always be sure of the quality of the steel.
However, there are some very good outfits that do a neat and tidy job with good materials. In your case, just swapping a straight pipe for a straight silencer, there's not a great deal to go wrong. In theory.
I'm just thinking you might be waiting a while for that particular Milltek silencer to come up second hand. I know you like your bargains.
At least look into it and find some feedback on local places before you rule it out :)