Affordable integrated pure class A?

Class A means very little - a high bias A/B can sound just as good.  Most rate their “Class A” rating into a 8 ohm load so if a amp is rated at 50W Class A into 8 ohms - that same amp will only produce 25W class A into a 4 Ohm load.  

Look into thd Yamaha AS series integrated amps - beyond excellent sounding units.

Nelson Pass wrote an excellent paper on Class A amps you can read it on the Pass DIY site

good Listening 

Peter 

https://www.passlabs.com/press/leaving-class

Here it is 

good Listening 

Peter