Share 'Budget Water Heater efficiency upgrades - What works best?'

A client of mine opted out of replacing his 20 year old tank style water heater with a Takagi TK3 instantaneous water heater because of the high price and wants to replace it with something of the same configuration that is not too pricey.   That puts the 95% efficient models out of the running. My question to you pros is, what is a good upgrade for a tank style water heater that is more efficien…