Maintain .NET Document Management System

Our in-house document management platform has been running smoothly on a C#/.NET stack, MS SQL Server, and AWS for several years, but the developer who built and nurtured it is leaving. I need someone who can step in right away, understand the codebase, and keep the application stable and performant... (Budget: $15 - $25 AUD, Jobs: .NET, .NET Core, C# Programming, C++ Programming, Database Administration, Database Development, Microsoft SQL Server, SQL)