I would *think*, could be wrong, that in that case your costs will be roughly the same of an average trainer in that era with that engine (for example, C152), with a few things added:
- Caring for/replacing the fabric
- Dealing with groundloop damage if it happens
- Insurance costs of a taildragger.. usually gets better with a bit of time as indicated above
From what little I know, the 235 is a very bulletproof engine and I don't recall hearing of many that don't make it to or past TBO.