Filter System Advice

I've been going through my old Le Mans photos recently, scanning negs to my computer and I was reminded that in the mid-90's I played around a little bit with effects filters. I still have one or two, but haven't used them for years and the Cokin holder I had at the time has long since disappeared.

I quite fancy having another go. I can buy another Cokin holder and adaptor rings relatively cheaply, but I wondered if there is any advice to be had about which way to go? I really don't want to spend a fortune on something that I may only use occasionally.

Thanks