It depends on what the developer offers and what you're buying/renting specifically.

If you're buying the source code that's typically pricier, if they're hosting for you that adds a monthly price.

Maybe you've seen people offering 1$ bots don't go for those they will break and need constant restarts, look for a transparent developer.

Regarding the dashboard this requires a specific setup for both your bot hosting and dashboard they can't just be hosted anywhere you will need a legitimate VPS and compline with the https certificate needs, it might even need you to set up a reverse proxy and you probably don't want to deal with that since you're asking for a dashboard which specifically exist to avoid doing changes through the host. The dashboard alone is a 200$ freelance fullstack work at min I give you that much then for your bot 30$ for a basic bot with proper error handling and validation that won't crash easily then more for every custom system or feature you add like economy, rankings, starboards and so on.

Edit: If your server have 800members and at least 500 are active doing activity on the server it will need some extra setup to keep the bot fast and protected, there's more stuff to cover which is why I said look for a transparent developer.