It varies enough to wreck a budget, so check before you shortlist. BambooHR puts onboarding in the cheaper tier — new hire packets, checklists and e-signatures are all in Core at $10 per employee per month, while it's performance management that requires Pro at $17. Core does cap you at 5 open job postings.
Others move the cost elsewhere. Enboarder includes onboarding in the base package but puts I-9, W-4 and E-Verify in a paid add-on, which isn't optional for a US company. Trainual charges a $1,000 implementation fee on every tier including the cheapest. Click Boarding starts at $10,000 a year on three-year terms, with implementation billed separately. Ask which tier onboarding sits in and what compliance costs on top.