Just about to do this job, armed with my trusty (and inaccurate) Haynes manual. Would not think of bothering with secondhand. Any local motor factor (Unipart, Halfords, etc) should be able to supply a pair of struts for less than £90 if you shop around. Mine is a turbo diesel, which has the gas filled struts so is most expensive. Prices have varied from £44 each and a little cheaper, but Halfords also want to sell me a fitting kit.
You will need spring compressors and a good tool set and some mechanical sympathy.
Couple of things to bear in mind. Haynes says replace the securing bolts once you have undone them (may be the fitting kit referred to by Halfords). One end is 17m and the other 16, and they are tight and good sockets and ring spanners will be required as the nuts are shallow and easily rounded. Also the bolts seize in the hub. I used heat to slacken 3, so replacement is a good idea.You will have to hit the end to free them, ruining the bolts. You will need to disconnect the steering arm to rotate the hub enough to hit them freely. Fingers crossed, as I am doing this next week