If price is an issue, you might consider UKOnline. To my knowledge, in the areas that they serve, they are about the cheapest discrete service (i.e. not bundled in with telephone services or cable or ...). As long as you aren't after blistering speed, they charge £10 per month for 1mbps, no download limit.
Yes, they supply a Voayager modem, but there is no reason to suppose this should be a problem (might it be your telephone line isn't up to scrath in some way?). In any event, you can always buy your own modem / router.
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