If you were keen on keeping rats you would need to buy them in pairs or more in single sex groups, as they are sociable animals. I'd try contacting rescues or trying to find a reputable local breeder in your area if you are keen on buying rats.
As for prices;
Missy was £7 (rip)
Boys were £20 for 4 of them, (I rehomed them from previous owners that wouldn't let me take them for free, even tho they were the ones advertising)
Cage (Terenziani Michealangelo) - £55
Giant Rolly Wheel for Rats by Savic - £15
Litter (Biocatolet) - £27 per year
Shredded newspaper/kitchen roll - £12 per year
Savic Sputnik XL - £6
2 Savic Igloos - £6
600ml water bottle - £2
Corner litter tray - £5
Pet carrier - £5
Cat scratcher - £6
Food - £60 per year on shunamite mix (works out £5 per month, £1.25 each)
Treats - £12 per year
Vegetables - £24 per year
Other accessories/toys - £50
I make toys for them from items laying around the house mainly and from old towels/clothes so I won't add them to the price..
Vet bills - £60 this year
I've spent around £500 keeping rats for 2 years including the above. I can't think of anything better to spend £500 on
