Wow, that’s a big increase. Times have definitely changed. I doubt that K-1s will disappear given high volume K-1 embassies like Manila. I’ve always advocated for spousal visa, it just makes more sense and provides better options for beneficiary when it comes to work, travel, and definitely faster time to naturalization.
(We had $190 - DCF I-130 in 2006, I think I-751 was under $400 in 2009, and N-400 in 2010 under $600? - been a while. Both I-751 and N-400 from start to finish in under 3 months Chicago field office. GC issuance was free (part of immigrant visa processing - perhaps a share of immigrant visa processing? but no way to know if you’ll ever get one in real life - I never got the first one and had to go congressional route to get it issued.)