Hard pity for a limited 5 star is 90 (your odds of actually getting to 90 is absurd; soft pity starts around 74 and goes up for every wish you drop after that) and you have a 50/50 shot of not getting your character. If you miss it your next 5 star is guaranteed to be the on-banner 5 star.

So worst case scenario is that you go to 90 twice. A wish is 160 primogems or 160 genesis crystals. If you haven't bought packs before it's ~81 wishes for $100 (though you lose that bonus afterwards) but if you have it's 40 wishes for $100. If you buy all the packs while you have bonuses that's just about 163 wishes for ~$201. This bonus resets every x.0 patch so if you haven't bought it but plan on going ham on future banners it's a thought. You get 300 crystals for Welkin which is $5/mo so 3600 crystals (22 wishes) $60/year and 90 extra primos a day for 30 days (2700 or just under 17 wishes, if you extend it for a year that's 205 extra pulls a year)... with the caveat that you have to log in every day to claim it. You can also use services that go through currency conversion channels to save you some money (there's a few, lootbar paimons bargains; not a whale so don't know how legit they are).

Unfortunately after you spend these companies know the barrier to doing it again is lower. Bad news is I'm still hearing 6.0 for Sumeru Chronicle (including Wanderer) and Flins, good news is I'm hearing Durin got pushed back to 6.2.