12-325v DC/DC Converter
Variable frequency drives use your H-bridge chopping idea to control motor speed but these don't give good sinusoidal waveforms. Uninterruptible power supplies (UPS) do a better job.

You may be forgetting that in some ways your boost converter is doing the same job as the transformer based inverter but will be more complex.

Start pricing out your basic design and throw in a bit for whatever your time is worth. Then compare that we the cost of a 500 VA UPS. ;^)