Argos still sell what they refer to a 'Tradional TVs'. They've got a 14" portable at �53.79 or a 21" flat screen (CRT) set for �97.89.
Remember though that the all analogue transmitters will be switched off in the near future. The sets I've mentioned above would need a Freeview set top box to receive digital TV. However Argos also have a 21" TV, with built-in Freeview, at �127.19.
The prices I've quoted are those shown on page 370 of the current Argos catalogue. Actual prices should be slightly lower, because of the reduction in VAT.
As others have indicated it's also worth considering the secondhand market. The British Heart Foundation have large charity shops which only sell furniture and electrical goods. All their TVs are tested and sold with a short guarantee. (You can see them working in the shop). I was looking in their Thetford shop yesterday. They'd got a few portables at �10, with most of their sets costing around �20 to �30. The majority of them looked like new, both in terms of the condition of the cabinet and the quality of the picture. You can find your nearest 'Furniture & Electrical' BHF store from here:
http://www.multimap.com/clients/places.cgi?cli ent=heart
(If buying secondhand, remember to check that the set has got a Scart socket, since you'll need it for a Freeview box).
Chris