Domestic US: PeptideTest or Chromate
International: Janoshik (most popular)
I recommend sticking with the same testing company the vendor used for the pep batch that you purchased as that is typically a requirement for replacement/reimbursement for a product that fails to meet the vendor’s guarantees. There’s going to be variations in test results across testing companies (for multiple reasons) and they can be enough to cause test failure for a marginally acceptable pep.
Most economical option for pep testing is to join a group testing server where multiple people share in the testing cost. Why pay $300 on your own when you and 29 fellow researchers interested in the same test results pay $10 each?