Your cheaper humidors are usually veneer over MDF. I don't recall where I've seen it, but contrary to what many believe, MDF is satisfactory at maintaining humidity once it is well seasoned. In fact, it may be more stable in fluctuating environments of temperature and or humidity where solid wood may shrink and swell more with the changes or wide differences of humidity between exterior and interior. The caveat is in the quality of construction. Obviously, a cheaper humidor will be using MDF, and some of the less expensive models may not have the tolerances needed to not leak.
You can find MDF humidors that work just fine. The better MDF versions will have a thicker lining of Spanish Cedar on the interior vs. just a thin veneer.

Solid wood is a piece of craftsmanship, but you will pay for it too. I still use a less expensive veneer over MDF humidor and it works fine. Like all wooden humidors though, they breathe and will require more maintenance than your airtight storage units like plastic-ware.

If your current cheaper humidor is working fine, I say stick with it.