1.) What is your testing methodology going to be (especially with respect to performance testing)?

2.) Are you also buying a functional testing tool? (WinRunner, SilkTest, Visual Test, SQA Robot, etc.)

Mercury's LoadRunner is very good if you want to construct very quick tests and run them without a great deal of performance model or workload characterization analysis. LoadRunner is not very good at simulating different access methods (i.e., modems) nor is it capable of altering these within a single scenario. LoadRunner is good if you want to supplement it with third party tools that help you gather metrics for various performance models. Handles iterations pacing and user staging very well (especially with 6.0). Licensing is a bear with this, however, depending on how it will be used. Transaction breakdowns and drill-down procedures are only minimally present. Good network delay monitoring (if you license it).

Segue's SilkPerformer is much better from a robust performance testing angle - but the learning curve might be considered a little higher. It is much more capable of multiple access methods as well as treating staged iterations as individual users. SilkPerformer can be used for quick one-off tests just as LoadRunner can but it has the benefit (in my opinion) of allowing for much more robust performance modeling scenarios. Licensing is pretty decent but still expensive. Good transaction breakdown but not always the best drill-down scenarios.

Rational has a series of tools (one of which is LoadTest) that is pretty good and offers excellent drill-down and transaction breakdowns. About on par, in my opinion, with SilkPerformer overall.

Each of these has a scripting language (with Segue's being, by far the most robust, but with more of a possible learning curve). LoadRunner's internal scripting language is probably the weakest. You can also look at companies like RadView with WebLoad and RSW Software with eLoad. They all have their fine points but it depends on what type of testing you want to do and how detailed your testing is going to be. It also depends on how much and to what degree you will rely on other third party tools.