You can try the poundshop/ Home Bargains (might be a bit early though) but for germination rates, you really can't beat a garden centre. That said, I've had some good bulbs over the years from various poundstretcher /poundshop type places.
Also take a look at the Secret Garden - I followed an ad on here and it looks pretty good: they seem to sell overstocks, so choice is limited, of course, and I don't know what their postage costs but they've got some decent sized cottage garden-type plants that are perennials (will grow again next year) - things like lupins, delphiniums etc - for £1.99-£4.99ish each, in pot sizes that would cost at least £6.99 in a garden centre. (I appreciate that sounds a lot, but a decent packet of seeds of 1 variety is £1.99plus, and then you need seed trays, various potting on pots, John Innes no 1 and no2 etc)
Only thing is, depending on where you are, you shouldn't plant them out in the garden this early, and without hardening them off-you really need to wait until most chances of frost have gone for that.
May be better to get some summer flowering bulbs in the next few weeks, plant those and then see what Secret Garden have on offer in late March/April. Or-buy now, and put them out in the day, garage over night etc til the chance of a cold snap passes.
Both Thompson and Morgan and Suttons do big packets with 4-5 varieties of nasturtiums in, for between £3.65.and £4.95- I always get these for more variety. I think they're bright and cheerful (and go well with marigolds) and are fail safe (unless you try fertiliser with them, which sends the leaves mad). Just soak them in an egg cup of water for 24-48ish hours before planting, so that they germinate quicker. You can sow in pots indoors now, or direct into the ground as late as August for flowers the same year.