Starting April, you'd have to pay $3005 of adjusment of status fees when she enters the US on K-1 visa and you marry. That's in addition to whatever fees you're filing now for I-129F and embassy.
For spousal visa, you'd pay similar fees at the beginning and only $220 for green card when she enters the US.
The difference is give or take $2500, that's how more expensive K-1 is compared to spousal visa.
Plus with K-1 she'd be stuck in the US for 6-12 months not able to work or travel. Some EADs come fast, while others take 9 months or so.
Essentially, if she enters as a spouse, you'd pay fewer fees and she'd be able to start working within few weeks of entering. Even if it's a small part time job, it can make a big difference. Plus, when entering on spousal visa she can travel internationally next day if she desires, while with K-1 she may get stuck for 6-18 months until GC or advance parole shows up.