Rather than being a junkshop gem, The Mods by Sandra Lawrence is actually an eBay gem - although "gem" might be pushing the point a bit.
It's a classic example of trashy 60s fiction - or should that be photo fiction, packed with staged period snaps to accompany the plotline. And what a plotline - Julie is a young mod girl, saved from a biker gang by the gang's leader, David. They fall for each other, but there are more problems than just the mod/rocker thing. Julie's brother happens to by king of the mods and isn't keen. And both David and Julie's fathers happen to have an ongoing feud, so they don't approve either. And with this being trash fiction, you can throw in some violence and tragedy too.
If you want the full rundown, check out my review of the book on the Modculture website. And if you're still keen, you should be able to find a copy for under £10 online.