17-4PH H1150 is only Rc 28-37 according to AMS 2759/3, and even 17-4PH H900 at Rc 40-47 is still within the capabilities of conventional machining process. I believe 17-4PH actually machines best in an H1150 condition. If no post machining stress relief is required, it is usually best to machine in the age hardened condition. For 17-4PH, AMS 2759/11 requires a stress relief temperature 100degF below the aging temperature. Also remember that if you are age hardening after machining, you need to allow for up to .0009 in./in. of material dimensional contraction.
To get an idea of heat treat costs, a few weeks back I purchased 24' of 3/8" diameter 17-4PH (AMS 5643) cond A cold finished bar and then had it heat treated to cond H1025. The material cost was $88 including shipping. My local aerospace heat treat vendor charged $130 for the lot, including paperwork. That works out to $23.90/lb total for a relatively small amount of material. The material was delivered to my house within 2 days after ordering, and the heat treater had the material ready for pick-up within 3 days after I dropped it off.
Here's a tip. If you are making multiple parts from a long length of bar stock, before sending the raw material to the heat treater it is best to cut the bar stock into pieces just long enough to machine a part from. Heat treaters typically have many different sizes of furnaces, and they usually prefer using small ones since they are cheaper to operate. Sending cut pieces of material to the heat treater will reduce your lot charge, and will ensure your job is not delayed waiting for a larger furnace to become available.