Can someone please explain to me how i could solve the following problem..

I am making a reservation system for a hotel, it's a school assignment. At the moment i am done with 50% of the job.

But i am struggling with something:

I made a system that can add rooms to the database.

Now i want to give prices to each category of rooms, there are 3 categorys anyways ( family, single and double rooms).
I achieved that, now i can give each category a price.

Let's say i want the family rooms to be 120, then i just tell them to be.

But now i want to give them that price just for a certain time period. 

How can i make sql give rooms a certain price for just a certain time period or certain day?

I don't know much about the date function of php and sql.., can someone please help me? I am inputting the date information by a html input date field btw.
Now i want to add that to sql, and give the rooms a certain price for a certain time period.