I adopted two bunnies December 12th and I have easily spent $500 on them so far. I had to get them both fixed though which cost me $255 in vet visits.
I use the oxbow hay like you mentioned and a big 17.00 bag lasted me 1 month, but since you have only one rabbit maybe it will stretch longer.
somethings I have purchased for them are
A pet carrier -27.00
A cage-100.00
A litter box(a cat one)-5.00
Food dish-10.00
Hay feeder-10.00
A smaller bag of hay 5.00
3 big bags of hay-35.98 ( I got one free)
Bag of food-20.00
Toys( be prepared to replace these very often because they chew right through them)-2-4
A hay mat-7.99
A hidey house 27.00 ( my bunnies don’t fit in the smaller ones)
A water bottles(mine came free with my bunnies though)
Treats-2-3
Cage deodorizer 8.00
Sponges for cleaning-1.00 each
I spoil mine though. I’m sure you could cut this cost down by a lot. They are more expensive than I originally thought. Not cheap pets to have.

Hi! My rabbit is not as big as yours so the cost for me may be a little less due to her eating less and urinating less but here goes!…

Carefresh litter: 22.00 (lasts over a month changing the litter pan daily but I do use a mix of carefresh with pellet bedding)
Aspen supreme pellet: 23.00 for 18lb (lasts about 3 weeks changing the litter pan 2x daily)
Feline pine pellet litter: 9.99 for 20lb @ Walmart (lasts about a month changing the pan daily) – I actually just switched to this and it’s way cheaper for same absorption and odor control.
Oxbow timothy mat: 5.99 (has lasted over a month but looks like I need to replace it within next 2 months)
Oxbow timothy chew sticks: 2.99 for 4 sticks (1 stick has lasted a month and still going)
Oxbow western timothy 90oz : 24.99 (lasts up to a week for daily unlimited feeding for up to 10lb rabbit it says on the bag but I cannot vouch for that for I do not have a 10lb rabbit hehe)
Oxbow Orchard Grass : 6.99 (lasts about 3 weeks only because she doesn’t like to eat it much)
Oxbow alfalfa hay : 6.99 15oz (lasts about a week or less for my 14 week old)
Oxbow oat hay: 6.99 15oz (lasts about 2 weeks)
Oxbow young rabbit pellets: 8.99 for 5lb (lasted free fed baby bunny for about 6 weeks)
Vegetables: I haven’t started mine yet I am planning to next week or so with my organic herbs I have. I happen to grow basil and a couple others I use for cooking so it doesn’t cost me much but I would just probably buy organic vegetables at the local farmer’s market or grocery store and usually it’s about 4.00 for 4oz of mixed spring mix greens and various others roughly about the same price for the amount of other organic veggies where I shop. I’m not sure but a grown rabbit needs 1.5-2cups on veggies I believe?

That is pretty much what I spend a month. Of course the start up was more because I needed a x-pen, cage, litterbox, etc. Vet bills can run high too for small animals. At least it appears that way where I live. It costs more for my rabbit to be seen than my dog. It will cost me about 100.00 through a HRS vet to fix my rabbit in 2 months but her normal vet in my town who she sees for check ups and what not quoted me 350.00 or more. So, I’d say go through a House Rabbit Society vet. Good luck!!! You must be excited!