When I first started to buy Ayu's stuff, GUILTY had just come out a few months ago.
I bought parts or her back catalogue (I only got singles I really wanted, considering there were over 40 of them and who knows how many editions) second hand online, using eBay or a middleman to buy from Japan. I had lots of money (disposable income lol) so in only one month I think I spent about $300 on orders. I went a bit crazy, I admit that! After I got a big chunk of it I slowed down a lot.
Now I just buy as they come out, although I haven't preordered MOON/blossom yet as I may wait for the HK press or a second hand copy to come up. I just can't afford it at the moment lol I definitely recommend getting her older stuff second hand as it's much cheaper than buying new on YesAsia.
If you want a good quality version without the price tag of Japan press, TW press or Korean presses are awesome
Just know that there is no USB pressing outside of Japan! ^^