Greenbucket, you need to get yourself down to aldi. Look on t'interweb first, but every year they have young veg plug plants at reasonable prices (I think it was £1.99 for 6 plug plants last year). They have offers on every so often, Sundays and Thursdays, but you need to get yourself there on the day if it's something thats dead cheap that you really want.
Lidl have deals too, I don't have one nearby so don't know what their deals are like. You could always try Morrisons (the bigger stores will have a 'garden centre' outside when the weather warms up, and some of the bigger ASDAs and Tescos are trying to get in the act, too. I don't think you can beat Aldi for gardening deals. I planted three raspberry canes out today (cost £3.99 for three of them), had to use one of their gro-bags to top up the soil (removed lots of stones), it was lovely stuff, almost black, and when forked over was lovely and crumbly, not a bit of woody stuff to be seen. Will be buying more of their gro-bags for potting things on.