All 3 of your choices plus and electric, solar, solar-gas, solar-electric, and geothermal water heater. Your existing natural draft water heater
cannot be converted into a fan assisted / power vented unit, unless it was designed for such venting.
For that you’d have to ask its manufacturer. My approach would be to look at all those water heater options from the financial angle. If you’re planning to stay in this house for several more years and you can invest some cash into it, consider something that will save you energy in a long run. Check Energy Star guidelines for water heaters.
Electric water heater would be the cheapest solution (to install), power vent equipped gas – second, tankless, and everything else it’s over a $1000. Personally, I would go with tankless water heater, or some solar combo (if possible), but this might not work for you.