Unless they are putting crystal meth in the beer no Kiki Dee conversions are likely. Neither is a playing of the infamous Guilt Machine LP on grounds that you couldn’t hoof sufficient drugs and/or find several weeks to play it in its hideous entirety.
I reckon that you could get Eminence 15" for £100, must be able to get some half decent 2" compression drivers for £250, albeit JBLs might be a bit of a reach.
If there is someone with woodwork skills that would be cheap. You could probably scrounge crossover components on here (or trade for beer).
So it’s stretching the budget, but it’s making something interesting rather than a shitty old PA speaker. Depends what they’re trying to achieve.
Maybe a stretch but a battered pair of KEF 104/2s for around that budget? Very sensitive, easy to drive for valve amps and will go loud without strain.
As per Hoops reply above my 201s could be made available and in your price bracket. These are Hoops 's old pair and have been well looked after since I bought them from him.
PM me if you want to know more
If you’re looking for sensitive then Wharfedales will give you that and some of them also have quite a flamboyant look. The big E-series ones are probably too pricey and the small E’s too, er, small. They were followed by the Vanguard and the Ventana which don’t seem to be so fashionable. This pair of Ventanas https://www.ebay.co.uk/itm/Wharfedale-Ventana-Speakers/323917234202 may need re-foaming but are otherwise quite cheap for 8ohms, 95dB/W and 150W capability. But they could be on the small side. The Vanguards were the same sensitivity I believe but bigger.
A mate of mine has a pair of those, I’ve not listened to them in any way critically - they are on the floor in his garage, where there is also a beer fridge and a pool table. My impressions are though that they rock, I have no idea what they are like at low volume.
I’ll get a better idea when I get chance to chat with Alex and Seb later this week as to how important the sound is and how important the visuals are to them. Obviously if you want both that pushes up the cost and I doubt they’re looking to invest much at this stage.