Hello,
If you have already an order, you probably have also already an account and you can upload your file in that account and the system will give you the price for this model.
If for some reason your model is not OK to give you immediately the price (f. ex when there are some problems with your file or it would be above a certain amount, the button to request for an offline price request will pop up.
If that doesn’t work, you can also send us an email via the contact page on https://i.materialise.com/en/contact
As the orders are paid for in advance it’s impossible to add further objects in an existing order.
I hope this answers all of your questions. Kind regards Lizy