Chatbase

Train a support bot on your docs in an afternoon.

If Chatbase isn't right

Intercom Fin in customer support
The support bot I'd try first. You pay per resolved chat, which keeps it honest.
Per-resolution pricing
Zendesk AI in customer support
Sensible add-on if your helpdesk already lives in Zendesk.
Paid plans; see site
Siena in customer support
Agent of Record platform for consumer brands — support, shopping and social agents sharing one customer memory. Proven on high-volume ecommerce CX more than DIY SMB chat widgets.
Outcome/intelligence-based pricing (book a demo; no per-seat helpdesk fee)
Freshdesk in customer support
Value helpdesk with Freddy AI; strong India/APAC support.
Free tier; paid plans available