Okay that's the size range of an holland lop, if you are going to own one a 5 kg (10 lbs) of hay will be enough for nearly 2 to 3 months. It will all depend on how big your bunny gets. I know when I had my french lop with netherland dwarf and holland lop they went through 20 lbs of hay every month. Now, I only go through a third of what I did in a month before and I have two bunnies
(netherland and holland lop) to feed.
https://www.amazon.com/Small-Pet-Se...=1&keywords=1st+cut+hay&qid=1587572637&sr=8-9
https://www.amazon.com/dp/B00ID70IE...1_3968196990801&aaxitk=b0iWH3oLOsmGkVa0XqwzZA
Myself rather buy 2nd cut hay because I react badly to the hay that get cut early. But first cut are supposed to be the best for bunnies, the price of the hay would be expensive for me if I went through a lot of hay at one time which I no longer do. But you only have one it will be within a good range for food.
You can also look at tractor supply/stores if they are called like that if they are selling bales of hay. They are often cheaper and can be in a better quality. Sometimes if you have a local pet shop you can find hay there. But don't know how usa works, because at my place they get hay from the locals farmers. Live in an area with a lot of horse owners