A blindfolded monkey throwing darts at a newspaper's financial pages could select a portfolio that would do just as well as one carefully selected by the experts.
(Burton G. Malkiel, "Random Walk")

Sounds good, doesn't it? But, in a famous experiment that has been running for 14 years (between a team of professional investors and journalists from the Wall Street Journal, throwing darts) the people beat the 'monkey' by 10.8% to 4.5% !
 

How to prioritise? Decisions. Decisions.

So, accepting that you are unlikely to have unlimited funds and that having a method for picking winners is a good idea, this leaves the question of what to do first and what to defer or leave altogether.
 

Prioritise on Net Present Value(NPV)

Leaving aside the infrastructure (you have to put that in), the most obvious technique for prioritising content and applications is to look at which items deliver the biggest NPV and do them in strict order. There are two problems, however, with this approach;

Firstly, putting a precise value on many of the items is very difficult. Secondly, the chances are that the highest NPV items are also the most expensive and risky to do (so a few may use up all your funds).
 

Strategic Alignment Prioritisation

As an alternative approach, why not try my favourite model for prioritisation, where each item is assessed for (a) value & (b) ease and placed on a 2x2 matrix.

Value, in this context, is derived from the strategic objectives of the organisation; This will normally include profitability (as most have this objective), but also softer measures like employee satisfaction.

Ease is similarly based on a group of different measures, which includes cost but also takes into account the inherent  difficulty and risk of failure. Prioritised items will fall into one of four quadrants:
 

Quick Wins

High Value, High Ease. Many of these items should be in scope for your portal project. As you are likely to succeed in implementing these and be able to demonstrate immediate benefits, they help to build confidence in the platform, the project and you personally.
 

Big Hitters

High Value, Low Ease. Most of the really substantial items will appear in this box. As the old saying goes, 'nothing worthwhile was ever won easily'. Your project should include at least one or two of these (for substance) but too many will use up all your funds and eat into your contingency, when things go wrong (so don't overdo it).