Martyns Cycles was forced to close for a deep clean last Monday after staff at a neighbouring business spied smoke and flames from the rear of the cycle shop premises early that day.
While the fire did not reach into the retail shop area, copious smoke did get in, leaving the premises reeking.
Martyns proprietor Brent Martyn said they had since reopened, but were still working through the aftermath.
"We’re just busy trying to reorder what we can.
"We don’t know the total figure yet, but it could be anything up to 100 grand.
"We’re not 100% sure yet of the figure, it might take a few weeks," he said on Tuesday.
He told the Oamaru Mail immediately after the fire there had been at least two recent suspicious incidents in the area reported to police.
Last week, Oamaru police said they believed the suspicious fire at Martyns was an "isolated incident".
In an update this week, police staff said the matter was still subject to "ongoing" inquiries.
Mr Martyn said on Tuesday he believed the police were "on the right track".
