Due to the benefits of high-volume production, it's actually often cheaper to buy an all-in-one printer (incorporating a scanner) than it is to buy a standalone scanner these days!
However the CanoScan LiDE 400 offers a decent 4800 x 4800 resolution and is definitely compatible with Windows 8.1. (Click 'See full specification' for confirmation of that fact):
https://www.canon.co.uk/business/products/scanners/flatbed-scanners/canoscan-lide-400/
Further, it's extremely well-reviewed across multiple websites and easily within your budget, at just seventy quid from Argos:
https://www.argos.co.uk/product/6931104