For a print run of that size, I wouldn't experiment with a deviation from a known matched quality. I usually find that a change in paper or ink always gives a fair few unacceptable results until I'm happy with the result.
I posted a while back on costs of printing, and have just recently got rid of my photo printer as it was costing a fortune.
I now pay less than 8p per photo where as before it was approx 50p per photo.
I even pay less again but that depends on the number of copies I want.
As for the ink amount, if your printer is anything close to what mine was like, I would suspect that more ink will be required, but again, that will depend on the quality of your prints.