It is very affordable when compared to other options. Plus, it is classic, simple and elegant. It is however, rough to the touch. Algae love plaster so it will need to be maintained weekly and washed with acid every 3-5 years.
Company profit: It's a better option to hire a plasterer direct than to contact a company. This will save you money, as it won't cost the company any share.
Accent tiling might be a better option to save money on tiling. You can finish your pool's water with paint, plaster or other cheaper materials, then put tile around the edges to make a statement.