You will need to be both the customer and sales associate.

Le/La Client(e)                                                        Le/La Vendeur(se)

Get attention

                                                                                 Respond

I need... for class

                                                                                We have some .... (3 colors)

I would like (to buy) this/that....

How much is it?

                                                                                 It's ..... euros......

Thanks!

                                                                                 You're welcome! :)