Yup, for the Air, if you start with the $999 (8/256, M1 7-core GPU) and $1249 (8/512, M1 8-core GPU) standard configurations, and then bring them to storage parity at 512GB, you'll find the 7-core GPU version is $50 cheaper, and this price difference holds across upgrade options. This is even more pronounced for the Education pricing, where the 7-core GPU version is $70 cheaper.
To the OP and others who are curious about this difference and if it's worth it… I'm leaning toward no. But, I am worried that this could be one of those Apple things where there are other downgrades that they aren't clear about, or that, at some point down the line, the 7-core versions get cut out of features because all the other M1 machines have 8-core GPUs and features get designed around that. I reviewed the technical specifications and saw nothing that indicated a disparity in capability at this time.
That said, my GPU use is limited to powering external displays (2) and wanting the UI to be smooth. I don't game, and only very occasionally put together a brief video. And on a laptop that is going to be thermally constrained due to its lack of a fan, I figure the cores would be throttled down under load anyway, so the 8th GPU core is unlikely to be missed. And we're talking about maybe a 10% or so difference in benchmarked performance. The A12X (7-core) vs A12Z (8-core) distinction in 2018/2020 iPads Pro provides a basis for speculation. In the 12.9-inch model, the 2018 had a Metal score of 10937 in Geekbench while the 2020 came in at 11754. That's around a 7.5% improvement.
I'd suggest, particularly if you're cash constrained, putting the GPU savings of the base model toward more RAM or storage. And I just really really hope that we don't start seeing "*except MacBook Air models with 7-core GPUs" in the notes for future OS upgrades. ??
(After much hemming and hawing, I pre-ordered a 16/512/7-core GPU for $1259 on the Edu Store)