What would it cost to build this trading SaaS from scratch?

Looking for real-world estimates…

It’s a crypto trading SaaS with:

Multi-exchange support (Binance, Coinbase, etc.)

Portfolio tracking + live trade execution

AI assistant (ChatGPT/Grok-style) that answers user queries like “What’s my risk exposure today?”

Telegram updates for trades, price alerts, etc.

Clean UI, setup wizard, secure API key management

A buyer has shown interest, but I’m trying to gauge: How much would it cost to build something like this today, realistically? And would you rather sell or go full SaaS launch if you had it?