Enough money to buy any reasonably priced GPU up to GTX 1080 Ti. What would you buy right now for mining? Already have multi-GPU AMD and Nvidia.
If you absolutely want to buy a card now as opposed to waiting until the next generation is available, I'd go with a 1070ti. They overclock much better than 1080s yet have nearly the same number of cores. Yes, a 1080ti will still be faster, but you can put some of the money you save today by going with a 1070ti towards a next generation card once they are available.