Xmas play costume - help

[crappyday2018]

I'm trying to find a 'colourful 70s' costume for my 11yo for his part in the Xmas play (don't ask). I have literally tried EVERYWHERE. The 70s costumes your can buy on amazon are more 'hippy' costumes. I just wanted flared trousers and maybe a silk/satin shirt.
I also don't fancy spending a fortune on it.
Does anyone have any recommendations as to where I could find anything? I'm in the UK.

I would take an existing shirt and trousers and make a colourful big collar and kind of 'flares' from squares of fabric to attach to the trousers from the knee down.

@Annandale I would but I'm rubbish at stuff like that and I don't have a lot of time. I'm sure his school make things as difficult as possible!

I must say I'd be doing it with cardboard or at best a stapler...

cardboard!! good idea - thanks!