is there a smoking ban in salou in the bars and restaurants? Are cigarettes cheaper to buy in duty free or in the shops there

It varies Louise, some bars allow smoking, some dont. Likewise some restaurants have a smoking/non-smoking area.

There isn't a blanket ban like we have in the UK. Spain, in my opinion, took a sensible approach, based on floor space / size of premises from what I can gather.

Cigarettes are cheaper in town as the Duty Free shop at Reus airport is about 5 euro per carton dearer.

You cannot buy fags or baccy in a normal shop or supermarket like in the UK.

You go to a licensed Tabac. Prices are fixed... only difference is what deal you might get on buying in bulk e.g. Buy 800 B&H and get half bottle whisky free!