Assuming the Bitcoin mining network as a reference to the state of the art: It would cost around a million US $ just for the cost of the electricity (8 cents p

Assuming the Bitcoin mining network as a reference to the state of the art: It would cost around a million US $ just for the cost of the electricity (8 cents per kWh) to impersonate you (1024 bit DSA). That could also lead to a MITM attack. To attack the encryption directly would take 65 billion $ in electricity alone. So fairly unlikely. So you would have to ask yourself what your messages are worth should you use OTR...