If you give it a while, some sort of cut and come again stuff usually gets given away free with either gardening or cooking magazine, in fact hasn't Gardeners' World Magazine got a load of seed on the front this month?

Failing that, I got two big packets from our local 99p place, Italian mixed and French Mesclun. The pack comes with vermiculite in to to help you keep the seed spaced out when sowing. I underestimated how much seed there was to vermiculite and now have a very full tray of seedlings. oops! still loads left in the packet though so a really good bargain

99p Stores - Quality Products for under a Pound!