to answer your question - from a non technical point of view. ;-)
a dvd recorder can create more than one sesssion on a dvd ... so in most cases you can record more than one prog on a dvd - subject to recording quality.
most recorders have a record quality setting ... so the lower the quality ... the more you get on a disc (my mum banks on 4 films per disc - and they are still very acceptable on her steam driven 26")
A definate enhancement to this system is the addition of a hard disc ... that way record and watch ... goes on HDD
record and keep ... goes on DVD
gor a sony for my 78 year old mum who recoeds almost everything ... and keeps most of it
record to watch ... and then decide to keep ... can be transferred from HDD to dvd later
look at a few - get some prices from the likes of empire direct
and if you go somewhere like comet ... or currys
http://www.comet.co.uk/shopcomet/category/972/ DVD-Recorders-with-Hard-Drive/pageNum/2/n/1000 972/numPerPage/10/sort/price_asc
when the assist says can I help?
open with something on the lines of ... I like this one ... but it's so much more than i could get it at ......
I can guarantee the assist will just nip off to see if they have any in stock .... and will return with at least a matching offer and might throw in a scart lead.