Cheap studded tyres for winter conditions, these are normally about £25 each. Available in both 700c and 26". These are the current on-one deal of the day (though were yesterday too, go figure).
These cheaper schwalbe studded tyres have studs offset from the centre of the tyre, so won't cope with extreme conditions as well as schwalbe's more expensive 'ice spikers'.
You can run at a slightly lower pressure than normal to bring the studs more into play on the straight at the expense of higher rolling resistance (though if you're a weight/rolling resistance cry baby then these tyres, and the relevant conditions you'd use them in, probably aren't of interest)
If your journeys are entirely tarmac you may be better off with 'winter performance spiked' or 'marathon winter' (less knobbly rubber grip with spikes), again these are more expensive but are also on offer at on-one currently.
There's also a 4 items for 3 offer on that you might want to check if buying any of these.