Halep has now reached a WTA final in 12 consecutive seasons after easing to a 6-0 6-1 victory over her teenage opponent.
The two-time grand slam champion faced Kostyuk at Indian Wells three weeks ago and was forced to come from a break down in the first set before prevailing in straight sets.
No such recovery effort was required in Cluj, with Halep progressing to her third final in Romania having twice won the Bucharest Open.
"I really wanted to play the final here. It's a home tournament and always when I come here, I feel great," Halep said.
"I'm really happy, motivated and I'm looking forward to playing the final tomorrow.
"I knew that I had to play a little bit faster, more aggressive and to open the court a little bit more. There [at Indian Wells], she didn't miss very much as she did today, but I think I took the ball faster and quicker, and the serve helped me today."
"I'm just trying to give my best, trying to be aggressive and enjoy. When I smile inside, it looks better outside. I have the whole country with me when I play at home, so that's why I'm motivated, that's why I feel safe and strong on the court, and I always want to play my best.
"I won twice in Bucharest and, hopefully, tomorrow's the lucky three, but if not, it's still a good result and it's good to be home."
Halep is unlikely to have it so easy in the final, which sees her face the in-form Anett Kontaveit, who will have added motivation on Monday (AEDT).
Kontaveit needed just more than an hour to defeat Rebecca Peterson 6-3 6-2, her 25th win in her past 27 matches.
Victory over Halep would see Kontaveit beat Ons Jabeur to the eighth and final spot at the WTA Finals in Guadalajara. However, Halep has won all three of their previous meetings.
At the Courmayeur Open, Clara Tauson will face Donna Vekic in the final after they overcame Liudmila Samsonova and Jasmine Paolini respectively.