Integrating real-time chat functionality into your Flutter-based e-commerce app can significantly enhance user engagement and support. Based on your requirements for an affordable and customizable solution, here are some Flutter chat SDKs to consider:

MirrorFly
MirrorFly offers a developer-friendly chat SDK with extensive customization options and over 1000 in-app communication features. It provides dedicated developer support to assist with the integration process.
SYNCFUSION

CometChat
CometChat provides a customizable Flutter Chat SDK and API, enabling real-time messaging and calling features. It includes pre-built UI components and a comprehensive feature set, such as one-on-one and group messaging, push notifications, and media sharing.
COMETCHAT

Stream
Stream offers a Flutter Chat SDK designed for in-app messaging with rich features like reactions, threads, media uploads, and offline support. It provides customizable UI components and core controllers to streamline the development process.
GETSTREAM

Sendbird
Sendbird's Chat SDK for Flutter allows you to build in-app chat with essential messaging features. It supports message threading, push notifications, and real-time event handling, with comprehensive documentation to assist developers.
SENDBIRD

TalkJS
TalkJS enables the integration of a customizable chat experience into your Flutter app using feature-rich SDKs and highly customizable widgets. It supports real-time messaging infrastructure suitable for various use cases.
TALKJS

When selecting the appropriate SDK, consider factors such as feature set, customization capabilities, scalability, and pricing to ensure it aligns with your specific use case and budget.