There is no set amount. The test is proportional: the committed funds are compared with what it would realistically cost to buy or create a viable enterprise of that type, and the money must already be at risk rather than merely available. For a small restaurant that usually means most of the start-up cost is spent or bound.
Price the business, then measure the commitment
Start by building the total cost the way a lender would: lease and deposits, kitchen equipment, leasehold improvements, licences, initial inventory, working capital for the first months. Use quotations and contracts, not estimates. Then set beside it what has actually left the applicants' control, with the paper that proves it: transfers, invoices marked paid, signed leases, delivery receipts.
The gap between those two figures is what the application has to answer for. Where the couple is uncomfortable committing before a decision, a binding purchase conditioned solely on E-2 visa issuance may use escrow to protect the funds pending the decision while still showing commitment, provided the assets are held for release once that condition is met. What can be managed is the order of spending, so that early commitments go to items that retain value if the plan changes.
Hypothetical example: a bicycle-repair entrepreneur and a treaty-national co-owner each put money into a proposed workshop, but their operating agreement gives a third investor veto power over daily decisions. The ownership and control documents may matter as much as the bank transfer. A first review should produce a nationality table, capital ledger, and management map.
It should also test whether the business can grow beyond household support. Failure commonly begins when an investor focuses on the amount spent but cannot show authority to develop and direct a real, non-marginal enterprise.