Look at Grand Endeavor (Jimmy Jacobs company but his son has taken over). They fall into that custom to semi-custom crowd. They will do full custom multi million but you can also select from one of their plans and sit down with a design person and modify to your liking for fairly cheap. We took their "cottonwood" plan, expanded bedroom sizes, deleted a dining room and added a bedroom and expanded the breakfast area, expanded porch etc and it cost a few thousand to have that changed/drafted, rather than 15 to 20k we were being quoted for start from scratch. Smaller plans and simpler finishes can get you in the $600s but can quickly run that up with the design person. But they definitely will let you make significant changes to plans and add custom features with finishes.
As with any builder your super and communication is going to be key. We had small issues but they worked hard to always resolve.
We used them in Canyon Lake out of their New Braunfels office but their main office is out of Georgetown and I know they work the whole greater Austin Area.
https://www.grandendeavorhomes.com/ 
