In that case:
Before I was collecting Pokémon, I was collecting Yu-Gi-Oh. I remember when I was literally doubting for roughly two weeks about a 28 USD purchase, which I ended up buying in the end after all. Iirc it was a SR Black Rose Dragon, somewhere in 2013/2014.
When I started collecting Pokémon, 50 USD each was indeed my limit for that initial order from TrollAndToad that started my Pikachu collection by impulse. This was mid-2015.
I think I upped that limit to about 100 USD each when I seriously started collecting all English Pikachu cards, just a few months later in Fall/late 2015. Early 2016, I decided to branch out into all languages and just collect everything, and I joined E4 after I came across Justin(ator)'s collection thread and website in February 2016.
I’m pretty sure that the first actually expensive card I bought was my first Art Academy Pikachu, which I bought from a fellow E4 member (the father of the winner, for the Japanese red raincoat Pikachu by Y. Fujishima, whom was active here at the time). That one was 300 USD, in August 2016. I bought the second Art Academy Pikachu on eBay for 320 USD not long after in October 2016 (the Hawaii Dancer one, which I bought from the brother of the Chilean winner).
I’m pretty sure that the first card that went above 1k USD was the MATCHPRINT Pikachu, of which only two copies exist. Before, I thought Rusty wouldn’t want to split up his set, and since he already sold one of the two MATCHPRINT Pikachu to Justin(ator), I didn’t bother to ask. But later on I heard he already broke up his set to sell his last two MATCHPRINT Charizard for 1k USD each, so I matched that offer for the Pikachu as soon as I heard about that, which he accepted.
Although it’s an unofficial release, I’m still very happy to have it in my collection. This was in June 2017.
Another one that was ~925 USD (so almost 1k) was the Pikachu with YOU Wagon promo, which I won in an Yahoo Japan auction through a middleman service in February 2017. This one dropped to a value of about ~100 USD half a year later, and it wasn’t until two years into the pandemic that its value was roughly what I paid again.. Nowadays it’s worth 1.75k-2.25k, though. 
The first card that passed 2k USD also passed the 3k+ threshold
, which was the PSA-10 The Masked Royal promo (for 3.4k USD) to 100% complete my FA Supporter collection (I paid 500 USD each for the PSA-10 Team Rocket Brief Case promos a few months prior, for those wondering).
There have been a few other 1k purchases soon after that, most notably more Art Academy Pikachu (cooking Pikachu by Rhivern for 1k USD and orange raincoat Pikachu by Sayaka Maruyama for 1.2k USD, which I both bought from another collector in January 2019, and the queen of heards Pikachu by Me!, which I bought on eBay from CollectorsCache for 3.1k USD in August 2000).
These days, 1k USD is a pretty normal purchase amount for newly released Pikachu cards, unfortunately.. I honestly lost count on how many 1k+ purchases I’ve already made, ngl.. 
The first card to be above 4k USD is still my second most expensive bought card, which is the German birthday Pikachu promo, for which I paid 3.6k euros (~4.4k USD with the exchange rate at the time) in May 2021.
And the first card to surpass 5k, which even passed 10k, and is still my most expensive bought card thus far: the English Art Academy kabuki Pikachu by Ashley, which I bought from a non-Japanese Art Academy collector (chibicollectables) whom upgraded his BGS-8 (that I bought from him) to a BGS-9. This was the final English Pikachu card I was missing to 100% complete my Pikachu collection in that language, a feat I’m still just one of two in the world to complete (after David Persin, the multimillionaire who used to collect all English cards). I paid 14k USD for it in September 2024. Apart from my house, it’s my most expensive purchase ever, even surpassing what I paid for my latest car (~10.5k euros iirc, which was ~11.5k USD at the time).
Assuming I have the money to spend again, I wouldn’t mind paying 15k USD each for the four missing Art Academy Pikachu or Pikachu SNAP, but considering the Art Academy cards are worth 150k-250k each and SNAP is worth 400k-500k, I doubt that will ever happen. 
So at this point, I’m not sure there are any cards I’d be willing to spend that amount of money on again. Maybe a future English Pikachu release, to at least keep that collection complete.
Although I honestly hope the prices stay semi-reasonable in the future. Apart from the Art Academy Pikachu cards, the English Pikachu releases overall aren’t too expensive. Then again, I’m not entirely sure. I’m completely out of the loop of values for cards I already own. Two weeks ago someone told me they bought a Rumble Pikachu for 400 USD for example, which I remember buying for ~10 bucks.
Should have bought loads of copies for loads of cards in the past… Hindsight is a b*tch. 
Greetz,
Quuador