You should definitely beware of those claiming you can get an A grade on GTMetrix with your current budget. I am a senior specialist in both SEO and web applications performance debugging, so I can assure you cannot get more than a B or C grade, actually. Honesty first!
That said, I can definitely help you to drastically cut off your current page loading time by optimizing code and resources on your site. This will improve the loading speed and increase your GTMetrix grade as close as to C or, hopefully, to B. For you to really achieve an A grade, you would require a serious, truly expensive, enterprise hardware upgrade, which is definitely out of your budget and of your scope (you don't really need it).
Feel free to reach out and I will be glad to assist you with anything you may need. I don't have any reviews yet because I've just signed up a couple of days ago, but I have a serious, long-standing, career with a consistent amount of skills and past experiences. Check your the project linked in my profile to get a glimpse of my capabilities.