There's not much to a transmission mount. Two pieces of steel suspended by a bit of rubber. If you are planning to fill the gap with a urethane product then it won't matter if it is a $16 or a $300 mount.
Don't use a urethane with a hardness factor over 35.
I suggest using a two part urethane mix because it cures so much faster. Less than 48 hours as opposed to two or three WEEKS (yes, I said WEEKS) required by the tube sealants.
Initially you might notice an mild increase in vibration at idle but after a few miles it subsides.
Engine and transmission mounts filled
The mesh is just some fiberglass mesh I had. I trimmed it away after the urethane skinned. Probably a waste of time but, it was there and I was there..