It's common enough if you keep your eyes open you might find something perfect.just during the week I got an old display cabinet with 3 glass sides ideal size for a viv for 50 euro.so if you shop smart it can work out a lot cheaper.no need for special glass even clear perspective will do the job.if you do go down the converting road just don't forget your drainage and ventilation.and give any paints or silicone plenty of time to cure before putting a cham in it