"This means we saved about RM2 billion," Najib said after launching the first phase of the MRT at Kwasa Damansara in Selangor.
According to him, all the contracts for the entire stretch of 51km Sungai Buloh-Kajang Line (SBK), also known as MRT Line 1, had been awarded and the works were near completion.
He also praised the project progress, which were completed in time and never once missed the targeted completion schedule during the five years of construction.
Najib also annonced that commuters can ride the MRT for free for a month, and charges for the service would come into effect starting Jan 17.
The free rides are also extended to feeder buses provided at the 12 stations along the 21km elevated line.
According to Bernama, the first phase of the route, which involves 12 stations covering a distance of 21 kilometres between Sungai Buloh and Semantan, would start tomorrow, from 6am.
The stations are Sungai Buloh; Kampung Selamat; Kwasa Damansara; Kwasa Sentral; Kota Damansara; Surian; Mutiara Damansara; Bandar Utama; Taman Tun Dr Ismail; Phileo Damansara; Pusat Bandar Damansara and Semantan.
The second phase of the MRT project, which will cover a distance of 30km and involve 19 stations from Semantan to Kajang, is expected to be fully operational from July 31, 2017.
With the launch, MRT Corp, the developer and asset owner of MRT, will officially hand over the first phase to operator Rapid Rail Sdn Bhd, the subsidiary of Prasarana Malaysia Bhd.
It was reported that the project delivery partner for SBK Line, MMC-Gamuda KVMRT Sdn Bhd had assured the construction cost would be reduced, without compromising on the safety and quality.
"If any of the job packages undertaken by contractors fall behind schedule, MMC-Gamuda was required to step in and help speed up completion," MRT Corp Sdn Bhd project director for MRT Line 1 Marcus Karakashian was quoted by New Straits Times as saying.
Also present was Transport Minister Liow Tiong Lai, Finance Minister II Johari Abdul Ghani, Minister in the Prime Miniser's Department Nancy Shukri and Selangor Senior Executive Councillor Teng Chang Khim.
The construction of MRT Line 2 or Sungai Buloh-Serdang-Putrajaya Line began on Sept 15 while the MRT Line 3 is undergoing feasibility study.
It was reported the MRT Line 3 is expected to cover Ampang Jaya, Kuala Lumpur City Centre, Jalan Bukit Bintang, Tun Razak Exchange, Bandar Malaysia, KL Ecocity, Pusat Bandar Damansara, Mont Kiara and Sentul.
Commuter will be able to use Touch 'n Go Cards to travel on SBK Line. Beside that, they can also purchase weekly and monthly passes, priced at RM2.50 and RM10 respectively.
Children under seven years old can travel for free, while the elderly, students and the disabled will enjoy 50 percent off the fares.
The MRT will operate from 6am to 12am on weekdays and from 6am to 11pm on weekends.