We learned quickly that the only way to control costs was to create a design which did not move walls, water lines, etc. You can get a pretty solid budget in front of you if you’re costing out “stuff”- plus installation- cabinets, appliances, etc. You will get a TON of “this is just an estimate” once you are dealing with demo, construction, labor variables. I got the kitchen I needed (cabinets were literally falling off the walls, and H is very handy so handled regular repairs as they were needed) but not the “kitchen of my dreams”- but it came in at budget, not over.
The horror stories you hear about the escalating costs are usually around “we moved the waste line and discovered X…” (whatever X might be) or “we knocked down a wall but then had to reinforce the foundation” or god knows what.
Keep it simple- replace what’s falling apart, upgrade the surfaces, invest in proper lighting so you aren’t slicing tomatoes in the shadows, buy really nice drawer handles- you’ll know what it will cost you before you sign any contracts. My two cents.