Can I prepare Gyuudon with normal rice?

I want to make Gyuudon for about fifteen people, but sushi rice is expensive. So can I use normal rice?

If by normal rice you mean your local rice variety then that will be fine, however an authentic dish would use Japanese rice. As you may know, gyudon is usually served over plain white Japanese rice (what some people generically call sushi rice), which is different from actual sushi rice (which is Japanese rice seasoned with vinegar).

Where do you live? If you live in the US, I found River white medium grian rice is acceptable for "gyuudon" (probably not for "shushi", though).

What do you mean by "normal"? You need to use short grain rice(sticky) rice for gyudon.