I think if you get many responses they'll basically say, "Do what works for you."
For reference, I'm an architect who enjoys visualization, maybe similar to yourself. I freelance visualizaton jobs here and there, when it makes sense. I'd say at a rate of less than one per month.
I've browsed the different freelance sites, but so far have not bid on many, nor won any contracts. It seems to mostly be people asking for 8 simple high quality renders of their proposed hotel and only want to pay $200. "If you know what you're doing it shouldn't take very long." If the clients looking for visualization services are at all like the clients looking for architectural services I suspect they don't recognize the value of your services and the skill it takes to accomplish their goals. Personally I would rather hone my skills working for free on a personal project than race to the bottom of a bidding war. If a client doesn't understand the value I bring as opposed to the lowest bidder from wherever, I probably do not want to work with them anyway. You may feel differently.
There are many threads on this forum about how much to charge. You need to figure that out for yourself, but I'd recommend not selling yourself short at the get-go.
Go Reds!