Hair Colour at Home - Please advise!

[newnameoldme]

Now I know the advice is always to go to a salon and I always do but...

I have moved city and my hair is suffering for it!

I had a really beautiful balayage but over the past 6 months I've spent more than £400 at 3 recommended hairdressers and my hair is really making me sad!

One hairdresser overdid the balayage refresh so I became more ombre 3 + 7. The last colourist persuaded me against a full colour change 3 and 4 and broke up the extreme two tone look a little, re-doing my roots 3 and blending some lengths 4. Then applied an ashy toner 6 to the ombre which gave me a khaki colour and after much persuasion fixed it with a more golden 6 toner. The result was not so bad but of course 4 weeks later the brass is back and I really feel as though I just can't face another expensive hair nightmare.

Is there a good toner I can apply at home? Should I try the 'salon hair' shop?
Failing that I'm tempted to just buy a semi permanent box with golden tones.