The Vendor may already have provided indicative pricing.
Sometimes that indicative figure is vague, or does not translate
to your situation, or is basically the recommended retail
price. You should ask what sort of discount can be expected.
Also request information on maintenance or upgrade costs.
Look at various components.
"If we purchase module A, what is the price? What if we also purchase module B and C?"
There may also be hardware purchases involved. Find out what are the likely cost of upgrading or purchasing new hardware. Also look at such things as installation, backup facilities, redundancy and the impact on licensing of these items. For example, if you have a backup system that can take over if the main system fails, does that mean additional software licenses.