hey mate, if i was you id head on down to the scrappers and get one, youl be looking at something more like fifty quid i would guesstimate, the easiest way to get a match would be to get an alternator off the same make/model as yours though other renaults may fit, the scrap man will often know what else might fit.
you can also try motorfactors for muchous cheaper aftermarket alternators, or have a look for companys offering reconditioned ones, if you cant get a local scrappys with the right one google renault spares and you will find national breakers brokers which can source for you, but whatever you do dont buy from the dealers unless you absolutely have to