Why the price of the car is only part of the risk
Insurers are pricing the chance and likely cost of a claim, not simply the amount you paid for the vehicle. the exact version plus version, repair costs, performance, theft record, safety and the type of drivers who commonly claim in it can all matter.
This is why choosing a first car by browsing the cheapest adverts can backfire. Two two similarly priced cars asking price may lead to quite different quotations for the same person.
get a quote for the exact car before paying a deposit
avoid depending on phrases such as “low insurance group” in an advert. Get quotes using the actual version you are considering. Engine, trim, gearbox and factory equipment level can change the rating or the insurer's view of the risk.
A useful buying order is: shortlist the car, check its history and condition, obtain realistic insurance quotations, and only then decide whether the total cost works.
The practical takeaway
If the insurance premium changes the affordability of the car, find that out while you can still walk away. The cheapest car to buy need not be the cheapest car to own.