Okay so some things I have noticed since 19.3 in terms of players and their skill/cost.
Marin has a little bit less potential now, where as his team mate Dani Olmo is absolutely bonkers after the update. Spanish kid who I always considered buying from Dinamo but never did, however I am guessing due to his real life play this season, his skill has been boosted and I am fairly certain his potential is right up there. He costs a bit - Got him for like 39 mill at the start of the second season, would guess he'd be cheaper at the start of the first. I don't like the 'tries to play way out of trouble' trait, but he seems to have really good versatility along with good determination, so learning new positions or traits should be viable. He is also good at free kicks which is a bonus. Definitely a must buy in my opinion, since prying him away from the Croatian league should be doable for most clubs if you are in a bigger competition and have some cash to spare.
Another Spaniard I consider a must buy, who was quite random stats wise but had loads of potential pre 19.3, is Pelayo Morilla. Good news is that he seems to now start with the same stat distribution whilst keeping the huge potential, however his determination can differ which leads me to believe that some of his 'hidden stats' can fluctuate as well. No matter though, he is definitely less random now and is always left footed, whilst being natural at AMC, AML and ML. I think his minimum fee release clause fluctuates from like 700k to 1.7mill from what I have seen. Not sure if that price depends on how high his PA has turned out. Was one of my favourite players pre 19.3 and is even more so now that he is less of an unknown quantity. Second season in one of my saves, after giving him more and more first team experience, and he is now labelled the next Pep Guardiola!
Tonali seems to be as brilliant as ever, and it is just a matter of hoping he gets a good roll in terms of his potential! So definitely a must buy, however he seems to cost more! So don't expect the 3-4 million dollar bargain.
It is hard to just name 2 more people as must buys! Since there are so many! However going by the ones who seem improved since 19.3 and someone who doesn't get much attention, I am going with the Brazilian defensive midfielder from OGC Nice Danilo. He has such good stat distribution across the board! Like almost to fault where he doesn't truly excel in any area at the start of the game, which is fine, because his potential seems to have been boosted. So he should develop into one of the better midfielders, specially when looking at defensive abilities combined with play making nous.
Last player I am going to recommend is another South American, however this guy seems to have come out of the blue. I went on a scouting rampage in Argentina after 19.3 - There are copious amounts of amazing players there *cough* Exequiel Palacious *cough* and they can be bought for peanuts *cough* Thiago Almada *cough* Sorry bout that! My favourite might be a left footed ball playing centre back who isn't at one of the more reputable clubs known for exceptional players like Boca *cough* Cristian Pavon *cough*, you will find him plying his trade at Defensa y Justicia. His name is Lisandro Martinez and he appears to be a MUST BUY!!!! Seriously there are hardly any talented left footed ball playing centre backs in the game, and he starts with amazing stats along with the 'tries long range passes' trait. I had to look him up on youtube, and sure enough he looks pretty talented in real life. His potential seems huge and could well be one of the best backs in the game. Now you can't buy him in the first season since he only just signed, or at least I haven't been able to but I don't play with any of the massive clubs, don't fret though! I bought him at the start of the second season for 2.6 mill! Maybe he would be willing to move in the January window, I did not try.
There are a lot of other great players who either improved or regressed after 19.3 however I am sticking with these 5.
Since I don't know how much it would cost to buy Danilo, here is a lil bonus beauty - Marcos Paulo from Fluminese in Brazil. ANOTHER non-eu player!?! Guess again he has Portuguese citizenship along with his Brazilian nationality! Rejoice!