We are doing this too. We found a designer that will work within our constraints.
While we haven't started construction, I have found cost balloons out of control because the desire to do custom or a little nicer here then there really adds up. We are managing every decision to our budget and trying to decide what is must have vs nice to have.
The girlfriend found ways to remodel bathroom and kitchen way under national or even Austin average but again within limitations. We aren't moving plumbing, limited structural changes, and going cost efficient on products. You have to be willing to do the day to day project management which is a pain in the ass and takes a lot of time. My job and the girlfriend's allows this flexibility.
One suggestion that we are pursuing is having the whole project designed and cost out but then phasing the construction and implementation so if we want to increase our budget / spend then we are not forced to right at that moment.
Feel free to ping me as we are spending every free minute planning, implementing our remodel.
Datapoint: We expect to spend under $5K on our design plans and have found legit designers to do it. Close friend did his house design plans for $3K and was a 3,000 sq ft house.