For the uninitated, the Th*rne seconds on epay have, thankfully, done away with the practice of some punters buying quantities of complete 'seconds' hives in the winter sale and marketing them on epay at extortionate increase after assembly!
Complete second quality hives are no longer offered in the winter sale, now.
CW,
As for double walled hives, a layer of expanded polystyrene is an easy alternative - likely more expensive over the life of the hive, but an alternative.
14 x 12s are more difficult for the new starter than the 'normal' deep brood BS, but a lot soon change to the jumbo format when they find that a single deep brood box is insufficient for most modern bee strains, after they are forced into the realms of a brood and a half, or double broods. A simple eke can be used for conversion, but new frames are the cheaper alternative (in the long run) compared to the 'convertors' some offer.
The first year is usually no problem (unless starting really early with a strong nuc), but the second year (when they think they know how to keep bees) goes seriously awry, when either having to contend with bees that swarm (due to space restrictions) or having to resort to using 22 frames for the brood nest.
All good fun and a steep learning curve at times. The internet is great, but only if the advice is absorbed and acted on. No real need for new beeks trying to re-invent the wheel!
No internet fora when I started, mostly old beeks still using single brood (or brood and a half, which they reluctantly told you about after the swarming problem arose)! So BTDT.
Regards, RAB