Stanchion wear is very rare on Maguras. They have to have been very neglected to get worn.
I would imagine you'ld be looking at £100+ or much more if the stantions need replacing. Magura don't encourage home servicing and replacement seals for newer forks are hard to find as a result, though Fox wiper seals will fit. Anything more and it's off to Magura.
For that sort of money you could pick up a nearly new set in fine fettle...
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