The most affordable mod with great battery life and a good chip is the Wsimec Reuleaux RX200 or the new RX200S, the only downside to it is that it has a shallow 510 connection so if the RDA has a protruding positive pin it might not sit flush or could damage the mod's 510 if forced flush, other than that it provides the best battery life in the market with a decent chip.
The other mod with good battery life is the SMOK KOOPOR Primus having 3 batteries setup in parallel but its Firmware sucks if you are going to use it in TC mode, but could be a viable option for variable wattage.