WTF, someone give that real estate agent the boot. Upside down photos on the property listing. Fuck me that's unprofessional.
Back to the question.
You can inject insulation into the walls on weatherboard homes. Or if you plan to redecorate, rip the internal wall lining off and insulate then. The cheapest DIY solution is to blow used polystyring balls into the cavity with a vacuum cleaner.
No photos of the attic rooms, but insulating the roof will be more costly than a traditional single story home. If the attic rooms have exposed rafters, a cheap solution should be possible. Polystyring sheets covered with a paintable surface installed between rafters.
Insulating the underfloor area should be easy and can be a DIY job. Use polyester wool and a staple gun.
It'd be worth insulating the windows. Timber frames allow for either secondary glazing (thin film or acrylic/polycarbonate sheet. Or go the whole hog and get double glassed glass.