Open with the problem you are solving, not a feature list. which contract model for software development people will use this, how many times a day, and what happens today? A vendor who grasps the purpose often proposes a simpler way to reach it; someone handed only a feature list can only price exactly what you asked for.
Set out the scope as short scenarios: who does what, livewire vs vue and what happens next. Equally important, list what is out of scope. An explicit list of exclusions saves more argument during acceptance than any other single page. Mark too which decisions are settled and which may still change — the difference changes the price, and concealing the open questions only hurts you.
Write down the hard constraints. These include systems you must integrate with, the data you already hold and its condition, security and compliance rules, user volumes, software development outsourcing models target platforms and any technology you are committed to. If there is a hard date, say what depends on it: a team can often resequence the work to hit it, but only if they know it exists.
Say what done means for each item. Testable acceptance criteria do not require any formal notation: a short paragraph setting out what request a project estimate user should be able to do is enough. This one section shortens the sign-off process considerably and eliminates the usual argument at handover.
To close, ask for a specific format. Ask for a breakdown by feature or module, the assumptions used, the risks the team sees and an optimistic and a pessimistic figure. Take a broad range as useful information rather than evasion: it tells you the part of the brief that needs work. Then clarify that area and ask for a new estimate — the second estimate will be far closer to reality.