Cheap Box Sets

Astaire is an unusual choice.  Not what I'd expect to be recommended here. 

Two sets that I've been considering:

Fairport Convention : 5 Classic Albums

Terry Reid :Original Album Series - Terry Reid  

Both inexpensive,  great music. But I'm unsure of the sound quality...

I'm surprised you're asking this, but just as a rough price point, I'd say that any brand new box set at $5 per disk or less is probably a pretty good deal. Assuming the sound quality/mastering or remastering are up to par.

Here's another contender:

Zappa - Meat Light - $8.71 + $4 Shipping from Amazon resellers (3 disks) 

There's another Oliver Nelson box set that I've been watching on Amazon. 

Oliver Nelson: The Argo, Verve and Impulse Big Band Studio Sessions Import
https://www.amazon.com/dp/B000FBIYHU/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=LARRM9BR2U0Z&...

Only 6 disks, fabulous music, selling for $199 used and $279 new.

Strangely enough, it can still be had from the record company, Mosaic, at $102. You gotta watch out for those Amazon sharks.

http://www.mosaicrecords.com/The-Oliver-Nelson-Verve_Impulse-Big-Band-Sessions-233/productinfo/233-M...