Your prospects needs solid estimate before making decision on investment. Call it a proposal, quote or Statement of work. Often we (vendors) sit on the fence, throwing numbers with bundle of disclaimers/assumptions. It does not help us nor the prospect.
Instead, step in, roll your sleeves and scope it. Learn about the business, read existing documentation, meet client team, get right people from your team involved in the process. Put dedicated time and effort to provide solid estimate for prospects. It is the foundation of which trust will develop and prosper!
Who should pay for scoping? Well, budget can be drawn from Presales, prospect, or negotiate 50/50. But do not sit on the fence!