Welcome to the forum... Where in VA are you?
Sounds like you have a classic under managed older pond that has become very eutrophic. The biggest question is: What are your goals for this pond? Once those goals are determined, then a plan of action can be taken. Ponds are holes into which money is thrown. Particularly if you want them to meet your expectations... The cost you are being quoted, it's hard to say what is reasonable and what isn't. If you live near by, I may be able to come over and give you some on scene advice. I don't own a pond management company and won't charge you a penny. I can at least get you started with some ideas and what you can expect to pay to accomplish your goals.
Thanks for the reply!
I'm down in the Richmond area, close to Ashland. Guessing you are a tad north of me...
Goals? Honestly...That is a great question. I've gone through a progression, neither of which are vetted and each without any real knowledge of what it would mean...
I started thinking about it as a fishing pond for me and the family, presumably bass. Then, when I saw the Koi in the pond and started to look into it I realized that maybe I could have a hobby raising/selling the Koi over time as they got large, etc. Now I'm sorta of at the point where I just want it to look and be an enjoyable part of our property while weighing the costs/maintenance aspects...Then it algae bloomed and now I just want that to go away.

So...I guess you could say I'm at least partially undecided, but if it made sense raising Koi (whether to sell or not) is probably the most attractive idea at this point...