There is no fixed dollar minimum. The investment must be substantial relative to the total cost of buying this business, so a modest price bought outright can qualify, while a large business bought with a small deposit may not. Government fees are separate and listed on official schedules.
Substantiality is a ratio, and fees are a footnote
Officers apply a proportionality test: the amount committed compared with the cost of purchasing or establishing the enterprise. For a lower-priced business, a higher proportion of the price should be invested, and buying the whole sixty percent stake with the applicant's own committed funds is a strong position. Money spent on the purchase price, equipment, inventory, lease deposits and working capital all counts once committed.
A loan counts if secured by the applicant's own assets, not by the business being bought. Separate from the investment itself, budget for the visa application fee at the consulate, the fees for dependent applications, professional fees, and any state contractor licensing and bonding. If the applicant is already in the United States in another status and seeks a change of status instead, the I-129 fee under the USCIS fee schedule (G-1055) applies.
Do not count professional fees or relocation costs as part of the investment.