I don't have a data source but I think this is an interesting question so I'm just going to share my thoughts on the topic. If you just compare unit sale numbers between a base model $13k Hyundai Accent or whatever against the sale numbers of the "average" Ford F150 (the top selling truck in the country) with a base models ranging from $29k to $52k, I'd suspect the mean/median spread probably isn't as wide as you'd expect.
I'm sure the spread plays a part but I think what's really happened relates to the prevalence of captive auto lenders (all the major manufacturers have subsidiary financial services companies), long-term loans and the increasing trend toward leasing.
People tend to buy the payment. I can pay $300/month and I WANT that. If I need to sign a 96 month loan to get that, that's ok.
If you take the average car payment over time and compare it to the average car price over time you'll see that it's the financial instruments available that have changed; car sale price has grown a lot faster than car payment. 10 years ago the average car loan duration was in the 60 month range and it's about to crack 70 months now. Even if you increase both numbers (payment and sale price) for inflation you see that the price has risen faster than payment. Really, low interest rates and longer loan durations have "bought" more average car than dollars have. Leasing has a similar effect.
From the Ford link in the comments above:
Demand for F-Series was strong all
year, with customers requesting the
newest technologies in our highseries trucks. High-series Super Duty
and new 2018 F-150 trucks pushed
overall F-Series ATPs to a new record
level of $47,800 per truck, $3,400
higher than a year ago.
An 8% YoY increase in average price is certainly not explained by the average buyer actually parting with 8% more money.
IMO, "average" new car sale price does little more than illustrate that on average people make bad decisions. Kind of like the "average" american diet when the "average" american person is overweight.