Actually, you posted your overhaul costs from 2016
here on PPRUNE. So something like USD 100k for the 12-yr inspection, luckily no biggies, no gearbox problems for example. Plus USD 250k for the turbine overhaul. Total therefore around USD 350k, but fairly unpredictable. For the next person it could be a hundred grand more, or even worse.
Compare this to fairly predictable USD 100k to USD 200k for a R44 overhaul (depending whether it is a 12-yr inspection only, or it coincides with the 2,200 HR overhaul). Plus some USD 10k higher insurance premium per year (makes USD 120k over 12 years).
We take your word for it that your operating cost in between the scheduled major services may not be that different between between a R44 and a EC120. You specified those to be around USD 10k per year. However, if you add the difference in 12-yr inspection cost (still USD 25k *per year* when spread out evenbly over the period), it would be misguided to believe that the cost of ownership would be the same. It remains hugely more expensive to operate a turbine (any turbine, for that matter). And that without counting the cost of capital, as you would bind some addtional USD 600k or so in that asset.
But of course, nobody has said the two machines are the same. For what the EC120 offers it's probably totally worth it. So you must enjoy!