Speed Up WordPress Site

My WordPress pages are taking far too long to load and it’s starting to hurt both user experience and search visibility. The slowdown is clearly on page-load rather than in the dashboard, but I am not even sure what caching or optimisation plugins—if any—are currently active... (Budget: $10 - $30 USD, Jobs: Google PageSpeed Insights, JavaScript, MySQL, Performance Tuning, PHP, Web Development, Website Optimization, WordPress)