What is offered is not always what they are willing to pay. Don't be afraid to ask the scheduler directly for more money. The worst they can say is "NO"
I usually don't work the first week of each month, and offer my services for a small increase the second week, and on the third and fourth weeks I offer my services for even more.
My attitude is, take my offer or counteroffer me and we can work it out.
TS has zero wiggle room and refuses to stop offering me work that is over 200 miles from my home, so all of their emails go into my spam folder. I have a few shops for them with direct contact with the schedulers when my turn for rotation comes around, otherwise the rest offered by them is crappy pay and I won't work for pennies.