Speed-Up Slow WordPress Dashboard

My WordPress front-end behaves acceptably, yet the admin dashboard crawls and occasionally throws a “website under heavy load” message. I have not added any new plugins or themes, and a caching plugin is already active, so the usual quick fixes have been exhausted... (Budget: ₹100 - ₹400 INR, Jobs: Database Management, HTML, MySQL, Performance Tuning, PHP, Web Hosting, Website Optimization, WordPress)