The Bangkok MP who has been disqualified by the Constitutional Court will have to return salaries and benefits worth around 8 million baht over the past two years.
Thai media reported on Friday the finance department of the House was calculating the amount Mr Sira would have to return to state coffers dated back almost 33 months ago, or from March 2019 to Wednesday.
The amount comprised Mr Sira's monthly salary of 113,560 baht, the monthly salaries of his seven assistants ranging from 15,000-20,000 baht each and Mr Sira's meeting allowances and travel expenses.
It estimated the total at 8 million baht.
The court voted 7-2 on Wednesday to disqualify the Palang Pracharath MP for Lak Si district after finding he had been sentenced to jail 26 years ago.
The ruling took effect retroactively on the March 24, 2019 election date.
The immediate effect of the ruling was PPRP would lose a vote, leaving it with 116. A by-election must also be held within 45 days.
Section 98(10) of the 2017 charter prohibits a person who has been found guilty by a final court ruling for certain offences from applying to run as an MP candidate. The court found he had committed "offences related to assets committed dishonestly under the Penal Code", one of categories listed under the section.
The ruling also had other repercussions.
Mr Sira would be banned for life from running as MP and return all the benefits he received under Section 101(6) of the 2010 MP law.
The leader of the party to which he belonged will also be punished for endorsing him as its candidate under the political party law. Uttama Savanayana served as PPRP's leader at the time.
In 1995, Mr Sira was sentenced to eight months in jail, halved because he confessed, by the Pathumwan Court on fraud charges in a case involving a car purchase contract.
Mr Sira claimed he later reached a settlement with the plaintiff (buyer) and paid him damages. Since fraud cases could be settled, the court disposed of the case, he argued.
The former MP also said he had not actually set foot in prison and was among those cleansed of any guilt by the 1993 royal pardon act celebrating the 50th anniversary of King Bhumibol Adulyadej's accession to the throne.
The Constitutional Court, however, found the plaintiff had never reached a settlement or withdrawn the complaint. The Pathumwan court therefore disposed of the case after the appealing period expired and the ruling became final.
The court also viewed the royal pardon law did not change the fact that he had committed a crime.
Pol Gen Seripisut Temiyaves, leader of the opposition Seri Ruam Thai Party and chairman of the House anti-corruption committee, was the first to question Mr Sira's qualifications. The pair, who sat on the same panel, were known sworn enemies in Parliament. The former police chief later submitted a petition against Mr Sira with the Constitutional Court through the House speaker.