Don’t believe the hype; the portal is not a silver bullet.
In fact, the technology itself is only one small part of the equation. As far as cost goes, the cost to buy and license a portal solution is often a fraction of the cost. The time to implement the technology and to develop policies and processes to ensure it works according to plan can take months if not years. And lets not forget about the plan; a portal needs a detailed plan with objectives and measurable goals.
Janus Boye explains why portal products are “much less out-of-the-box” than expected in Enterprise Portals: Tip of Which Iceberg?:
There is an important caveat to all the generalizations above: portal implementations frequently differ with respect to scope. Some portals are designed to span an entire enterprise, while others seek to fulfil a specific business mission, often at a departmental level. Not surprisingly, different vendors target different scenarios. All vendors in the Enterprise Portals Report call their products "enterprise portals," but the reality is that they do better and worse across different use cases and vary substantially in complexity and cost.
Consider as an example the popular Microsoft SharePoint Portal Server, which may be a good fit for workgroup document sharing, but quite weak for e-business and self-service scenarios that involve participants from beyond the enterprise.