Is there a limit on the price a founder can sell the business to an Employee Ownership Trust for, or on how much they can discount it?

In the US there's no EOT-specific cap or floor on the sale price. Unlike an ESOP, where the Department of Labor under ERISA bars the trustee from paying more than appraised fair market value, a US Employee Ownership Trust runs under ordinary state trust law, so the seller and company set the price far more freely. The real limits are standard IRS fair-market-value rules and what the business can repay. Discounting, even partial gifting, is allowed.