First decide what sort of thing you want, ie a particular plate with your initials, something non-specific oe a 'prestige number'. Then have a look at a number of the sites (the same plates often appear on several, and a lot of places are part-time home run businesses)) and see if the asking price is within your budget (bear in mind that plates are often vastly overpriced), so take your time looking and comparing.
I'd been looking for a plate for a while, and came across one that suited, but it was priced at £2k, which I thought stupidly overpriced, £500 was the max I'd pay. I phoned the up, offered £400, which the refused. 3 weeks later they phoned back, said they'd take £650, and negotiated down to £450. Its a UK plate K8 xxx where the xxx is my daughter Kate's initials.
