Does this sound reasonable for Bridesmaids?

This is my first time here so, hello!
I thought I'd ask opinions on bridesmaids/mates attire.

So I'm having two friends with me, my best friend of over 15 years as Maid of Honour, and a very close friend as my bridesMATE. I say mate because he is transgender. My MoH isn't very feminine either so may not want to wear a dress. Because of this, I want to ensure both of my bridesmates are comfortable.
I have an idea to let them know what colours to look out for, and then let them have at it. I don't want to pin them down for something they don't want. So they can choose an outfit and style they're happy and comfortable in, all I'd ask is that they'd let me see too to see if it matches our theme well enough.
Here where some may disagree with me; I would ask them to buy/hire the outfits themselves. Especially if it's something they can use at other events. I'll be hiring my dress (or buying second hand) since we're trying to be thrifty and environmentally friendly. I'd ask to see if they want to do the same to save them money.
Our wedding is in 2 years, so I feel it's plenty of time to save up for an outfit. Especially since my fiance and I have asked for NO GIFTS. This would be the ONLY thing they pay for since we're covering everything else.
Is this a reasonable request? I've never had to plan a wedding and only been to my aunties back garden ceremony as a child so I don't know how things work. Be gentle with comments!