I think the comparison is invalid primarily because the Western equipment has enormously bloated price tags. While there is definitely a lot of money going into Ukraine absolute dollar wise - the vast majority is in bloated Western arms or money directly for the support of military conflict. The $400 million skimmed off just to buy (Russian) diesel is just one example.

Let's not forget that while the US itself had 500K troops in Vietnam at its peak - the South Vietnamese army was a bit less than twice that size. So we're talking about nearly 1.5 million troops - 500K US and 950K ARVN. This is much bigger than the entire military of Ukraine - probably by several multiples.

On the other side: the North Vietnamese were not just fighting with AK47s. There weren't man portable SAMs then, but the North Vietnamese had artillery, tanks and so forth even if much less than the US or ARVN. Dien Bien Phu fell not because of AK47s but artillery. Similarly, while the US troops in Vietnam weren't getting hit by ballistic, cruise or hypersonic missiles or air launched bombs - they were getting hit by mortar and artillery. The Easter offensive of 1972, for example - Wiki shows the PAVN (i.e. North Vietnam army) losing hundreds of tanks.

Did the PAVN build these? No, they came via train from China and Russia.