There is insufficient publicly available evidence to confirm that it is now cheaper to buy a new car made in the UK, EU, or Japan than one made in the US.
It will now be cheaper to buy a new car made in the UK, EU, or Japan, than one made in the US.

High new car prices mean used cars are being kept for longer - Auto Express
Source: autoexpress.co.uk
Key Evidence
The recent US-EU trade deal imposes tariffs that could influence car prices but does not conclusively make EU-made cars cheaper than US-made ones.
General reports on high car prices do not address geographic manufacturing cost differences.
theguardian.comtheguardian.comTrump and von der Leyen announce US-EU trade deal
No direct price comparison data was found.
What the Evidence Shows
The claim asserts a comparative cost advantage for new cars manufactured in the UK, EU, or Japan over those made in the US. To evaluate this, one would need up-to-date data on new car prices by country of manufacture, factoring in tariffs, supply chain costs, currency fluctuations, and recent trade agreements. The search results include references to a recent US-EU trade deal involving a 15% tariff on most EU exports to the US, which could affect pricing competitiveness but do not provide direct price comparisons.
Additionally, an article notes high new car prices generally leading to longer retention of used cars,theguardian.comtheguardian.comTrump and von der Leyen announce US-EU trade deal but does not specify geographic manufacturing cost differences. No direct evidence or authoritative data was found comparing current retail prices of new cars by manufacturing origin. Given the complexity of automotive supply chains and pricing influenced by many factors including tariffs, production costs, and market demand, such a broad claim requires detailed economic and market analysis that is not present in the available sources.
Therefore, the claim cannot be verified as true or false based on the provided information.