After the toys and cage, the most expensive foods seem to be pellets and nuts. My ekkie doesn't like pellets much so it’s not too bad. He loves nuts though and they can be fairly expensive depending on what you are buying.
I offer a around 4-5 different fresh fuits/veg and a frozen veg mix everyday (4$ for a bag that lasts nearly two weeks). I sometimes offer brown rice as well, which lasts for yonks in the pantry.
You will need to be prepared to spend some money but its not really that bad. For example, obviously you won't need to give her say a whole apple each day, you can cut it up and keep it in the fridge, so you have 3-4 days supply of apple for the cost of 1

. If I had to give you a rough estimate of how much I buy for the birds, I would say 1 piece/punnet/bunch of each fruit/veg a week. So maybe….around $10 a week just on fruit veg and then the occasional $20 on nuts and pellets. (in AUD$)
Having said this, the biggest expense by far is the vet bills. It’s not too bad if birdie stays healthy, you only need to pay for checkups. But if she gets ill, you could be looking into triple figures for treatment and meds.