You won't know the quality unless you can confirm what source the eBay seller is using for the wire. There is plenty of low grade, cheap
stainless wire on the market from China
and who knows where.
This is not an area to cheap
out. Break a wire you will probably lose your mast
which will immediately eat up all the money
you saved going to eBay and a lot more. Or the wire starts rusting prematurely or grows a few fishhooks requiring premature replacement; again, there goes your savings.
Then there is the time you spent, boat yard time, loss of sailing time and more if you have to repeat the job.
Buy good wire from a reputable source.