I've literally just ordered a spiral cutterhead from Byrd Tools in the states (assuming you've heard of them) for my DeWalt DW-733. £490 (incl. 40 extra cutters and shipping), then import charges whatever they'll be, then a day's work fiddling to get it in but, to me it seems worth it. I'm firmly a hobbyist but probably ramping up in the year.
I'd be lying if I were to say the potential for showing off wasn't a factor.
Look into Byrd Tools though, the more commonly produced cutterheads are cheaper. I think the only portable thicknesser that's available in the UK, that they offer a cutterhead for, is the DW-733, but there may be OEM clones out there under different brands that might work.
You can also supply them with a drawing with all the relevant dimensions marked out and they will produce one for you. Marius Hornberger of youtubeland has done this and I recommend having a watch.