I have always used a pan head self tapping screw without problem. I get mine from Winzer Wurth but they don't have website. Screwfix do a similar screw
They work for me just as well as the 'proper' screws at a fraction of the price. The important thing is that you don't want a countersink screw as it splits the wood.
If you want square drive, then, since Mc Feely's (well respected seller in the US) want about $30 per 000 for their bog standard finish 1 1/4",
I suspect that £9.00+ is the UK equivalent of rock bottom.