Can't do PEI. but can do PETG, which is what I use for my 3D Printed enclosures, this has a similar heat resistance and strength to ABS. One offs are not cheap. You're looking at £20/hour design time, it'll take probably a minimum of 5 hours to do what you want, plus print tests and the final print. Depending on print time that can be anything from £7.50 to £25. At a minimum you're looking at at least £150 just for one enclosure. Of course if you're willing to 3D Model it, I'm happy to print it out.