Provide alternative for fast_gas_price - for slower but cheaper transactions (aka: lowering processing fee)

[Deepcryptodive]

Currently, the processing fee suggested by the front end is calculated according to the following formula:
operation_fee = 1.1 * gas_per_operation * fast_gas_price * eth_price_in_dai (or chai),
where fast_gas_price is provided by Gas Station Network.

At the time of writing this comes down to a $9.9 tx fee for a simple DAI transfer (at ~145 Gwei for fast_gast_price). For many applications, this is prohibitively expensive.

Can an alternative be provided for users that do not require fast transactions?
e.g. using the average_gas_price from the Gas Station Network?

(Source)

Potential issue: The "time to live" for messages signed using stablecoin.services is currently 10 minutes. This might need to be increased, to accomodate for slower confirmation.

[MrChico]

Thanks for the writeup. This is indeed an accurate description of the situation. The fast gas price is chosen simply for being the most reliable to ensure that the tx will eventually be included and not dropped from the mempool. The backend is simple threaded right now, so it would need to be improved to be able to deal with different tx speeds. Another simple solution would be to set the default speed to avg for all transactions