Below is a compact, practical shortlist of affordable omnichannel messaging options for enterprises — grouped by how they help lower total cost (pay‑as‑you‑go, low per‑seat SaaS, channel/CPaaS specialists, and self‑hosted/open source). For each I list why it’s cost‑friendly and the most relevant public pricing or model (so you can compare quickly).

Pay‑as‑you‑go / usage-based (good if you have spiky or seasonal agent activity)

• Twilio Flex — Highly customizable contact center with an hourly model (good for seasonal scale) or predictable named‑user option. Pricing: $1 per active user hour or $150 per named user/month. (twilio.com)

Low‑cost per‑seat SaaS (predictable, fast to deploy)

• Freshdesk (Freshdesk Omni / Freshdesk Messaging) — Full omnichannel helpdesk at competitive per‑agent tiers (Growth/Pro/Enterprise; omnichannel plans often start in the $29–$109/agent‑month range depending on tier). Good balance of features vs price. (freshworks.com)
• MessageBird Inbox — Simple agent seat pricing with volume discounts (example: $30/seat/month for 3–10 seats) and unified channel handling; channel usage (WhatsApp/SMS) billed separately. Good if you want a managed omnichannel inbox with clear per‑seat costs. (messagebird.com)
• HubSpot Service Hub / Conversations — HubSpot offers free Conversations and low‑entry Service Hub tiers (starter/professional/enterprise) that scale into enterprise capabilities; useful if you already use HubSpot CRM. (Starter and up start at single‑digit to low‑double‑digit $/seat promotional rates; Enterprise seat tiers are higher for large deployments). (blog.hubspot.com)

Channel/CPaaS specialists (lower messaging/WhatsApp costs at scale; good when channel fees matter)

• Gupshup — Strong for WhatsApp and high‑volume messaging with low per‑message fees (Gupshup charges small per‑message platform fees in addition to Meta’s per‑message rates); useful if WhatsApp/SMS traffic is your biggest cost driver. (gupshup.ai)
• Infobip — Enterprise omnichannel with flexible plans and channel traffic billed on top; public starter price shown from ~€39/month plus channel traffic — good for global reach and negotiating volume discounts. (infobip.com)

Open‑source / self‑hosted (lowest software license cost; higher ops work)

• Chatwoot — Open‑source omnichannel inbox you can self‑host (no license fees) or buy hosted plans; their hosted enterprise plan is ~ $99/agent/month if you want managed support. Best when you can run apps in‑house to minimize recurring SaaS spend. (chatwoot.com)
• Rocket.Chat / Mattermost (with omnichannel connectors) — Self‑hosted chat platforms that can be extended to handle multiple channels and keep license costs low (more infra/engineering effort).

How to pick the most affordable option for your enterprise

1. Estimate real volume: agent hours, monthly messages per channel (WhatsApp/SMS/email/chat). Channel vendor fees (WhatsApp/SMS) are often the dominant cost. (WhatsApp pricing models shifted toward per‑message in 2024–2025, so check current per‑message rates for your countries). (gupshup.io)
2. Compare total cost of ownership (TCO): platform seat or hourly fees + channel (WhatsApp/SMS) fees + implementation/maintenance + integration costs.
3. If you have developer resources and want lowest ongoing SaaS spend, consider self‑hosting open‑source (Chatwoot) and connect CPaaS for channel delivery. If you prefer low ops and predictable SLAs, choose a per‑seat SaaS or a CPaaS + managed inbox bundle.
4. Negotiate enterprise volume discounts for messaging and request bundled quotes (seats + channel traffic) — many vendors will reduce per‑message or seat rates at scale.

Quick recommended picks by use case

• Spiky/seasonal traffic: Twilio Flex (hourly model). (twilio.com)
• Fast rollout + predictable per‑seat cost: Freshdesk Omni or MessageBird Inbox. (freshworks.com)
• Lowest software license cost (can own infra): Chatwoot self‑hosted (+ CPaaS for channel delivery). (chatwoot.com)
• If WhatsApp/SMS costs dominate: evaluate Gupshup, Infobip or negotiate with MessageBird/Twilio for volume pricing. (gupshup.ai)

If you want, I can:

• build a 1‑page TCO template you can drop your agent counts and message volumes into (hourly vs per‑seat vs self‑host) and compare 3 vendors; or
• shortlist 3 vendors from the list above and draft exact questions to send to their sales teams for comparable quotes.

Which follow‑up would help you most?