Well it depends how you define "cheaper"
If its just monthly payment then yes like for like it will be less on a new car because they subsidise the finance. When I was looking at the golf / M135 they were both 6% APR but you are sill financing a much higher GFV at the end of the day.
In the end I bought a used 135 coupe and paid higher, but I also negotiated a lower rate - down from over 12% to under 10% APR.
There aint no free lunch at the end of the day and manufacturers sell new cars because of the lower monthly payment making it "affordable" to get into a new car. Ultimately if you PCP a car costing £30k new v a £20k car used (which i went for) you still pay less for the used one, a lot less. Plus with a new PCP you can normally put in max 30% deposit, with used I was able to put in 40%.
If i was going to be doing high miles, I would buy something 2-3 years old, lower than average mileage with a much lower GFV to buy it outright, then its easier to sell on. But I understand some people like to change the car every 2-3 years and buy new, but you ultimately pay a lot for that, especially if doing high miles.
I learnt a lesson though running a BMW 330ci for nearly 3 years, it cost £6500 used and I sold it last week for £4500. That really was cheap motoring and it never missed a beat, plus personally I like the feeling of having a car "bought and paid for".
When I bought the 135 (30 months old) I could have had a new one for less monthly payment because of the good deals on offer, but ultimately I wanted to pay it off so bought used, with a lower start point and a 24 month PCP with a much lower final payment that I know I can make in 2 years and have the car paid off.
Pays your money and makes your choice..