[Derision]

Well, if you want to do it where the #bot spawn command is processed in bot.cpp, you could add this around line 12424:

                if(!c->HasMoney(c->GetLevel() * 1000))
                {
                        c->Message(13, "You don't have enough money to spawn a bot.");
                        return;
                }
                c->TakeMoneyFromPP(c->GetLevel() * 1000, true);

That would go just before the existing line:

Bot* TempBot = LoadBot(botId, &TempErrorMessage);

At that point, the variable 'c' is a pointer to the client that is trying to spawn the bot.

Note that the HasMoney/TakeMoneyFromPP methods take copper as an argument, so 1000 is 1 platinum.