Especially if said qualification is only a 'certificate' and not a degree-level one?

I'm thinking about doing one in web design but i don't really want to shell out over £1,000 and 18 months of my time if it's going to get me nowhere.

I'm pretty sure that the course would get me the skills I want but would it actually be a worthwhile addition to my CV and would potential employers/clients see it as a proper qualification?

I can't do a full-time/part-time uni course as I don't have the money, so does anyone have any experience of this type of thing?