Being a bit of a bore, I would suggest that scrimping on your cups will devalue the beverage you serve. I accept that you are opening an Internet Cafe, so coffee may not be at the top of the list on expenditure, but if you are investing in an expensive coffee machine, it could be futile to then get the cheapest cups possible. Also remember, even if you can seat 50 people, they won't all be drinking coffee at once so you could reduce the number of cups by half - and increase your budge that way.
You could give Simon @ quickfire a try
www.coffeecups.co.uk, shameless advertising but should be OK in the forum as I am not affiliated to them and just think Simon is a nice guy (and has done some real nice decorated cups for me on a number of occasions.)
Rob.
Long forgotton Tech and Coffee Equipment guru.
Twitter: @c0ff33a
As I walk through the valley of the shadow of death I take a look at my life and realise there's none left 'Cause I've been brassing and laughing so long that Even my mamma thinks that my mind is gone