If you had your own router, attached to the ISP's cable modem, and are moving to ADSL, then you need either:
- An ADSL modem with ethernet connection, used with your router or
- An ADSL modem/router.
Is that Â£30 for a modem, or a modem router? - if it's a modem router, go for it - you can get them cheaper, but using theirs would mean less aggravation in case of problems. If it's a modem only, then forget it - Â£30 quid is insane.
Trawl ebuyer.com , and you can find modem-routers for Â£19.99 or less, but watch the descriptions - a "single port" requires an additional hub or switch to support multiple connections.