Custom Closet?

One cost effective way to do it to use normal stock doors on the closet which can match other doors in your apartment. After that as long as you do not care about finished wood sides and back, you can use a website like below and any carpenter can cut to size on site if/as needed. If you want finished back and sides, you have to find a millshop who will do a small project and it is not going to be cheap.
https://www.modularclosets.com/?channel=Google&gclid=EAIaIQobChMI1rKgq_7g5QIVwf_jBx0OHAmcEAAYASAAEgKmNfD_BwE

You can find an Ikea specialist that can design and install Ikea materials that are fairly high quality. If you just want a basic laminated particleboard, we used a place called Anthony's Closets on Long Island for a large walk in closet that I would call functional and perfectly fine, and if I recall less than half the estimate we got from California Closets.