What do you want from an (isolation) transformer besides it having the minimum voltage/current/power(/frequency?) specs that the to be isolated device needs? Does it matter whether the transformer is being used to perform precise measurements, to prevent for getting in contact with live circuitry or something else?
The reason why I'm asking is that for a 230V isolation transformers that can handle at least 2A current, I've seen isolation transformers starting from €60 for a bare transformers to well over €200 for units that are in some kind of enclosure and have medical grade specifications. While my primary motivation for an isolation transformer is working on power supplies it would be nice if it is not a single purpose tool.