There is no fixed amount. The investment must be substantial in relation to what this particular business costs to establish and operate, so the benchmark is the enterprise, not a threshold figure.
Proportionality is judged against the venture
The test is relative. For a service business bought as a going concern, the reference point is the purchase price; for a start-up, it is the cost of establishing an operating business of that type. A landscape installation company needs trucks, trailers, mowers and specialised equipment, a yard, insurance, licences and working capital for a seasonal cash cycle, and a plan that funds all of that is on much firmer ground than one that funds a fraction and hopes for revenue. Costs left out of amateur plans include equipment maintenance, seasonal payroll, vehicle insurance and the first winter. Nonimmigrant visa fees and any reciprocity charges are set out in official Department of State materials and should be checked when the plan is priced.
Hypothetical example: an indoor climbing-gym purchaser focuses on the purchase price but forgets the cost of inspections, insurance, route-setting and working capital. The proportionality analysis looks at the business as acquired or created, so prepare a budget that ties each outlay to the launch plan and proof of payment. The first review should separate funds already tied to a real commercial obligation from reserves that remain under the investor's control. Decide whether the total commitment supports the stated operation, rather than choosing a number first and backfilling a plan. There is no universal dollar figure that resolves the question across different enterprises.