Jeld Wen doors as well as most painted tube particleboard doors can nowadays be purchased without hesitation for 100-200€ net per door and frame; here you get a very good mid-range door for private, double-sided heated indoor spaces. Differences exist in UV resistance as well as in the chemical composition of the paints and hardeners; the RAL color shades can easily be determined online. The coating should always have good adhesion strength. I would not recommend buying doors at hardware stores; usually, the doors are stored upright, which can cause them to warp, a slight bow in the door may not be noticeable at first but then the door no longer closes nicely and does not sit evenly against the seal. It is also advisable to work with a professional when installing doors. If they deliver the doors themselves, you have a warranty; if they only provide the doors, you have no warranty on the material through the fitter, here the good service of some craftsmen pays off in the end. Buying doors in the hardware store and having them installed by the "specialist" therefore involves risks. Better to make a call, arrange an appointment, get one or two offers, and commission the carpenter with the best price-performance ratio and experience. ;)