Amazon has the ViewSonic VX2252MH.... just £76... I think its a great display.
21.5" Wide Color a-Si TFT Active Matrix LED 18.7" horizontal x 10.5" vertical, 21.5" diagonal
Full HD LED 1080p 1920 x 1080 resolution
2ms ultra-fast response time. Built-in 2W x 2 stereo speakers
50M: 1 ultra-high dynamic contrast ratio
HDMI input with VESA mount
I'm fairly sure there is a 24" version that should fit your budget.