The purchase price, working capital committed to the business, equipment and inventory count. The family home, personal savings held in reserve and refundable deposits do not.
Keep a schedule of what is spent, what is committed and what is only planned
The investment is what the buyer has placed at risk in the enterprise. The purchase price held in escrow on visa-conditioned terms, funds already spent on equipment or inventory for the business, and working capital transferred to the business account and committed to operations all count. Money the buyer keeps in a personal account as a cushion does not, nor does a residential property bought for the family, nor a deposit the buyer can recover at will.
Government charges sit outside the investment: the consular application fee for the E-2 visa, or the Form I-129 fee in the USCIS fee schedule (G-1055) if the buyer changes status from inside the United States, are costs of the process rather than capital in the business. Professional fees for the purchase and the application are private costs to budget separately. Present the numbers as a dated schedule so the substantiality analysis can be checked line by line.