Well, at least get rid of the grey for a couple of months. I've been using this particular product which I think is pretty good. Its called JUST FOR MEN. It doesn't take long to color my hair black, but from my many occasions that I have used it, I have always had to perform the process TWICE to get it to work better. The package inside includes the coloring treatment for two treatments in a short time between each treatments.
I think doing the coloring yourself will save you a heck a lot of money in the long run. I like this product, I normally get it from Zellers. Sometimes, they have a sale, and you can get it for C$3.50 per package from the normal price of over C$6.00 per package. Anyway, that's my two cents on coloring your own hair.