The cheapest solid core I can find is an $84 Jeld-Wen: https://www.homedepot.com/p/JELD-WEN-32-in-X-80-in-Hardboard-Flush-Unfinished-Solid-Core-Hardwood-Interio

The cheapest solid core I can find is an $84 Jeld-Wen: https://www.homedepot.com/p/JELD-WEN-32-in-X-80-in-Hardboard-Flush-Unfinished-Solid-Core-Hardwood-Interior-Door-Slab-45605/202036049 https://www.homedepot.com/p/JELD-WEN-32-in-X-80-in-Hardboard... In contrast, the pieces I mentioned above are $16 ($6 ea. for the MDF, $2 ea. for the 2x4s)