Give the person a breakdown of the cost in writing. The down payment should cover the cost of supplies you will be using. Are you quilting it? That's at least a $130 charge. You have to wash the tee shirts, another charge. Tell them to think about it and there is no rush because you have lots of other projects going. Chances are you will never hear about it again. My last write up for a nine patch queen size quilt with two borders with wool batting was $950 including the quilting and binding. The woman was a little taken back by the cost I had for fabric. I took the woman to the quilt shop where I bought the fabric. She was shocked at the price of yardage. She thought it would be about $30 for quilt fabric for all of it. LOL

Could you say - "I have thought this over long and hard - I do not want to do it -( or
'Doing this will not work out for me') - I am returning the t-shirts."

The less explanation, the better.

If you want to research other people that might do it for her, you could give her a list of possibilities.

I've also been asked to do a t-shirt quilt. I went online and found prices anywhere from $17 to $30 a t-shirt to do a completed quilt which included all materials, quilting and time to do it all. For 18 t-shirts that would $300 at the lowest rate. Go to wimberlyquiltstudio.com and under their quilting services go to t-shirt quilts and check out their prices. I'm doing 12 quilts and quoted a price starting at $250. I haven't heard back from the customer. The quilting would be an overall panto crossing over the t-shirts and no t-shirts with embellishments. Good luck if you decide to do this. I also try to avoid requests for t-shirt quilts.

I can't find any t-shirt quilts on etsy that are actually $100. When you look further, you have to select how many shirts in your quilt, and the price goes up and up. If you don't want the job, just say so and tell the co-worker to look online.

good point............$$$ up front

It's pretty easy for someone to say, tough, I'm not paying that later .......
........and then what do you have? Nothing but a quilt that has no meaning to you ...
....... and even if you are a Packers fan, you would have a hard time enjoying it,
as such, only seeing it as a bitter reminder.

Added problem you have is that this is someone you work with ...
and could create challenges for you with them or others in the working group.

My DD's friend asked how much it would cost for me to make a T-shirt quilt for her. I quoted a price of $800.00 just off the top of my head because I did not want to make that quilt. I never heard back from her.

Oh I do plan to price this accordingly.
I'm one of those people who if you throw me a couple of compliments and I cave every time.
example; several years back I took a cake decorating class just for fun...got good at it ....made enough $$$ to buy all my books for college with wedding cakes.
so word got around at work (I work in a very large Hospital system) and it snowballed into a monster!!!
definitely became Not fun.
Transferred to another department after graduation, and I don't dare let these people know about my cakes.

So I've positively decided any more requests I'm absolutely to busy

I will not let the cake decorating scenario happen again.

I know someone locally that makes t-shirt quilts and she charges $400 for a large lap size quilt. People pay it. It’s probably a good idea to figure out how much work and time, and determine your own price. I’d personally be careful about charging too little because you could end up with more requests than you want. But I guess you already figured that out!

I’ve made several, and they take a lot of time. A lot. Tell her it will start at $600, not including fabric and supplies. She has to go with you to choose and pay for those.