Really? ~400$ is not a reasonable amount to pay for good sound?
One would expect that with all the price drops that we see in electronics, during the years (due to competition, eastern mfrrs, etc), it would be a good amount for a good 2.0 set..
BTW, why did you mention specifically vintage amplifiers?
Modern big box gear is mass produced with a thousand bells and whistles crammed into a small enclosure. With all the extras forced in there, actual sound quality is often sacrificed.
Vintage gear was made to perform one duty only,make music sound good. Period.
If you were to spend 400.00 on a new amp/receiver vs. the same amount on a vintage piece,the SQ difference would greatly surprise you.
For passive speakers $400 doesn't buy you much of anything brand new, they will probably have an odd sound signature (probably muddy bass and thin midrange) and will not compare to anything good that you can get as studio monitors in the same price range. $400 is a reasonable amount but this is a hobby that is not about reasonableness in the new market.
Monsterzero basically explained one of the key differences in the vintage vs new debate. The other reason vintage amps are tough is because they will often need some servicing to correct age related issues and that will bump the price up.