From recent Experience , the best bang for buck new comes from the Elkhart Deluxe at under £500 in Straight fixed neck form, I don`t know if the two-neck version is as good, the Deluxe one piece is a superb horn for the money with excellent intonation and a smooth sound ...... I had the rarer Bronze body version of this and it was excellent, I'd still have it now if it wasn`t for my poor thumb joint not being able to take the strain so have to stick to Curveds (Centre of gravity and all that).. Sax.co have these
I have a 15yr old 300 series Curved which is even better made but has a brassy almost trumpet sound (which I like because its different) , I don`t know if later models of the 300 are as well made or sound the same .. Worth looking out for used .
on the subject of Curveds, the JohnPacker 043C curved is very good for the money new , it`s not as well made as the Elkhart Deluxe and series 300 (Chinese rather than Taiwanese) but sounds sweet, plays well and intonation is very good too , a great choice if you want a curved which sounds more like a Straight ...
I`m a tenor player who`s pretty new to the Sop but was put off Vintage Sopranos by reports of severe intonation issues (and Sops are an issue in that respect at best) though haven`t played any vintages like the Buescher you link to personally so only going on researched information. I stuck with modern horns .