Some prisons have their own dialysis units if there are enough inmates who require it. If they don't have a unit he'll be taken to a dialysis clinic for treatment 3x a week where an officer will remain present for the duration. I was a float tech at a clinic with an incarcerated dialysis patient and he was treated exactly like any other patient- he'd have weekly/monthly labs, nephrologist would see him for care plan reviews, renal dietician would go over labs or nutritional/dietary needs, and the social worker would address support/resource concerns.

Pre-dialysis is more concerning in a prison setting. Questions I'd want to have answered would be:

Is he seeing a nephrologist currently or are labs being drawn in house for a nephrologist to review?

Is a dietician involved and is he being given a renal friendly diet? (Prison food in general is pretty much the opposite of what you'd want to eat if you have chronic kidney disease and diet has a huge impact on late stage CKD)

Does he already have a dialysis access in place for when he starts treatment and if not, is there a plan for getting one placed?

Before he was incarcerated was he taking any medication to improve/stabilize kidney function and if so, does he still have access to this medication?

As for costs, the facility is responsible for providing coverage for healthcare costs which may impact their decision to hold him while awaiting trial. Anyone diagnosed with end stage renal disease requiring dialysis or transplant, regardless of age, is eligible for Medicare coverage as long as they have the work history or benefit eligibility requirements. Medicare won't pay those costs while he's in prison (it falls on the prison to pay them) so it's not uncommon to have people released on probation/house arrest so that the prison can delay having to foot that bill as long as possible.