Taxpayers were charged $390,000 to upgrade a coffee cart in the press gallery of the federal parliament, officials have told Senate estimates.

Officials from the Department of Parliamentary Services told a hearing on Monday that the kiosk was predicted to boost sales from 85,000 coffees in 2018-19 at the old coffee cart it replaced to “well over” 100,000 this financial year.

Caffeine addicts in federal parliament are served by four outlets: one privately run cafe called Aussies; and three run by the department – the Queen’s Terrace cafe, the staff cafeteria and the press gallery coffee cart.

On Monday the department’s secretary, Robert Stefanic, told Senate Estimates that the department was happy with the $420,000 (including GST) spent on the coffee kiosk upgrade because it was “well below” the $538,000 proposed by an independent quantity surveyor.

“The total cost – including the design, planning and construction – was just slightly over $391,000, rounded,” Stefanic said.

He noted Labor senator Kimberley Kitching’s observation that the cost was equivalent to “100,000 cups of coffee”, saying: “That’s about a year’s worth of sales, so as a return on investment that’s not bad.”

Asked about complaints that the kiosk was blocking access to lifts, Stefanic said it should not because a tensile barrier directed the queue down the corridor, away from the lift.

Kitching rounded out her questions by suggesting the upgrade was unnecessary. “I think everyone was fairly happy with the old one,” she said.

Stefanic said sales had increased due to higher volume of customers and greater choice of products. In 2018-19 the old cart sold 85,000 coffees and collected $330,000 in revenue, although Stefanic noted that year’s results might have been down because of the federal election.

“The current estimates for sales would put that well over 100,000 for this financial year, based on forecasts,” he said.

Liberal senator Paul Scarr congratulated the department on an “extraordinarily good result, on any objective basis”.

In 2017 department officials were forced to defend a proposed 70% rent hike for Aussies from $87,000 to $150,000 a year.

Officials told Senate Estimates the proposed increase resulted from the cafe’s licence not having been market tested in 25 years and encouragement from the audit office to maximise the return to the Commonwealth.