Planet X have a stack of cheap helmets that are good. Ive got 3 of them. Given up spending mega money on a lid. They are good for gravel rash protection.
The sizing at PX is right. Just measure your head, and if nearer large, get the large. Medium won't go on my noggin.
I had a stupid off a couple of days ago and headbutted the floor. Helmet stopped gravel rash on my forehead, but not my lip and chin, nor both elbows, knee and the nasty gash in my forearm. Gravel rash on the scalp isn't funny.
Gone are the days when I'd buy the latest Bell super expensive helmet (£150) when a £15 PX one is as good and you don't worry if it needs to go in the bin.