Best High Value, Low Volume Payment Processor

I've just bought a US based business (B2B) that processes about 60% of its revenue via card(invoiced/no card present). This ends up being around $450k per year. There aren't many transactions but each transaction is between $4k to $10k. I'm currently negotiating custom pricing with Stripe but was wondering if anyone knew of other companies that they had negotiated good pricing with.

Thats a high ticket price for cards / CNP. Risky too. Have you looked into option to convert some good amount of those via ACH or maybe bill them via bill.com so bill.com (that maybe they can better trust) to take it out via direct debit from their bank via ACH?

Which pricing do they offer to you?