Develop a custom customer portal

I am currently using Microsoft Dynamics NAV ERP and need to develop a custom customer portal.
The fact about ERP should not matter since any solution that works on other ERPS may also work for Microsoft Dynamics NAV ERP. This is because Microsoft Dynamics NAV has full web services support. Do not worry if you have no knowledge of Microsoft Dynamics NAV ERP, the most important part is that you have experience implementing developing such a portal for any ERP system. Experience developing a vendor portal would also be relevant.

Client will login and perform the following
(1) View their Contracts to see when their service contracts expire, last time paid last time billed etc.
(2) view and pay their invoices

At this stage, I am not looking for a proposal to develop the portal. I am looking to evaluate possible tools to use to develop the portal. If I chose your approach, I will pay for further analysis time to come up with a proper specification and cost estimate.

For this part of the project all I am expecting is for you to propose the kind of tools that you would use to implement such a portal.

Example of responses:
(1) I have used https://www.b2bwave.com/ to implement a customer portal for Oracle ERP and I can use the same to implement a customer portal for Microsoft Dynamics NAV
(2) I have developed a custom website to implement a customer/vendor portal for Netsuite ERP and I can use the same to implement a customer portal for Microsoft Dynamics NAV