u can try to modify mini fridge box - by adding another feet or two of height to original box - may not be professional but u can possibly have temp chamber for around $50 (depening on type of material u decide to use ) plus cost of a mini fridge around $ 100 - 150
Are you suggesting increasing the height of a minifridge? My recollection is that typically there is a refrigerant line that runs across the top, which is why you must be careful when installing a tap tower, so adding height would not seem possible unless you were to splice into the refrigerant lines and then re-charge the freon. Doesn't seem worth it.
But I may be misunderstanding you.