I'd say $5k is on the low end if you're having someone do this for you. My friend did something similar & they ended up paying 10k.

That pic in op is my wife's cousins house lolz

I did my kitchen in my old house myself. Doing filler pieces, under cabinet trim, built the island, and I can say that it's not as easy as it looks. If you don't have the right tools or have never done it before, you might just wanna pay up.

Yes, the reality is 7.5-$10k too rich for my blood

If I DYI, it will definitely be the Ikea route. No way would I attempt this from scratch. I'd get a lot of help from my father but even then, my schedule doesn't permit it.

The only thing is I'd like to change out the fireplace, which is a little more than just slapping some Ikea boards together and setting them on either side.

Also, I don't think there is any ikea product that achieve what you are looking for unless you have someone come in and trim it out. At that point you might as well go custom, not sure the savings will be there and you will get the exact shelving/spacing and no filled up cabinet holes, touch ups, blah blah.

You will see a lot of DIY items online, some do great work, others not so much. All depends on your level of OCD and what's acceptable and what isn't when it comes to fine details.

If you go on Pinterest, search for IKEA hacks. Some people have done a nice job of adding trim and mouldings to the Billy bookcases. It may not look as nice as the fully custom, but it's a fraction of the cost.