What is a polite way of telling customers they are just asking for too much?

I am a photographer and have very low rates to get my name out there. I have a customer that just seems to want it all and financially I can't afford to travel too far or buy more props or do some other things she is wanting. I do not want to come off rude, and I don't want to really lose her business either.

I use to go far out of my way for everyone but I am realizing that it doesn't help me at all.

Thanks for the help.

I had this problem during my 38 years painting murals. People can go crazy! Also- no! I do not repair walls before painting a mural! I noticed that I did better giving them limited choices. They might change a little but they tended not to get so confused.
In your case- I think you need a pricing paper- to show what each level of pricing includes. Be very specific. At the bottom, you can add- after this many miles away- add 40.000 for gas. Or time. After 3 props- add this. After 4 backgrounds add this. Then if you decide to let them have it for free, they think they've got a deal. I always had them initial it- one for me, one for them. I kept that in their file with the sketches, samples and bids and deposits etc. Don't steal from yourself because you are nice. I did that too. I was always honest and did more than bid so everyone was happy but did raise my prices and get signed bids or such.
Perhaps approach your (current?) customer with " Usually, anything over this many props or distance is a additional cost. I don't want to charge you, I know how budgets are , so lets do "this" (whatever this is) If they don't like that or think its rude, well- they are out for a freebie. I've delt with those too. Good luck!