Ignoring the cost issue for now, the GP4KSII 28-622/700c is known to run significantly wider than labeled, but I don't think the same is true for the 25mm versions. I've used the 28s, and they were pretty close to 30mm on modern/wider rims. I've never used the 25s, but I've also never heard that they were similarly oversized.
I've used the GP5K in 28 and 32. The 28 is pretty accurate to size on wider i19mm (19mm inner width) rims. I'm assuming the 32 is as well, since it's under 31mm on narrower i14mm rims.
Conti seems to have introduced a 30mm version of the GP5K as well, it's shown on their website now, but I haven't seen any offered from US retailers yet. Though I haven't checked recently, maybe they're trickling into the pipeline?
Lowest price I've seen the GP5K at is around $40ea, used to be a pretty regular price at bikecloset.com. They're o/s on 28/32 now, showing a $50ea price (rounding up the penny here). Really good tires are seldom any cheaper than $40ea. I don't think covid has helped increase availability or lower pricing.
https://bikecloset.com/product/conti...ute_pa_size=25
Best buy on light/supple tires right now IMHO is Soma's blowout of non-tubless Supple Vitesse SL tires, limited widths/colors, at $30ea. I use a lot of these, and find the 28s run as marked on wider rims, and 33s run a little narrower than marked. But it seems like they're down to 28 & 38 in black/black only now.
https://www.somafabshop.com/shop/pro...?search=supple
I'm only seeing 48-700c listed there for new tubeless Supple Vitesse SL/EX tires now, guess they're waiting for more from Panaracer?