Hair and Makeup

If it is optional you do not have to pay for it.

If it is optional then you don't have to pay. You'd only be expected to pay if you were requiring them to have their hair and makeup done. I would get a quote from the stylist then let each person know how much it will cost and to let you know if they are interested in one or both services.

If you are requiring your bridesmaids to get their hair and makeup done, you should cover the cost. Otherwise, if you are letting them decide whether they want to get their hair and/or makeup done or do it themselves, they can pay for it if they choose to have it done.

My girls have an option to pay for hair and makeup. If they don’t pay, they have to do their own or have someone else do it. I can’t afford to pay 150 per girl for hair and makeup

It is always optional. Fewer will want full pro hair and makeup if done onsite. I have always found nice the weddings I have been in with a large bridal party to have everyone responsible for their own hair and makeup, done in their own home or salon or hotel room.If 2-3 want to do it together, fine. But taking care of themselves all at the same time, in their own bed and bath, or salons. And coming together 1/2 to one hour before the ceremony, groomed and dressed. The recent trend of everyone gathered together to get ready, taking turns and waiting for hours and hours, Is a misery. I have started refusing to be in weddings where large getting together group stuff is the thing. No one's wedding is worth being in, if it takes hours and hours hanging out and getting ready. I have been in 2 weddings this year and 4 last where the bride was the only one who was more than 1 1/2 hour to get ready, in their own shared or inividual room. Mostly an hour, or an hour plus having been an hour in a salon for hair earlier for a couple moms. Everyone can do what they want earlier, alone or with another WP or family or SO. For a few years I tried doing what brides who wanted, the new trend of getting ready in groups. About 4 years, 6 weddings, in the midst of 25 years of ones where people take care of it themselves. I thought it miserable, 4-6 hours with a group I was fine with for 2, only to the start 6-8 hours more together for pics, ceremony, and reception. I came to each ceremony ready to leave, and said never again.
Even when age 14 or high school and college, I never liked hours or a bunch of women doing hair, makeup, and manicures. The traditional routine of everyone deciding and paying for ( or not) themselves Is by far my preference. And I do not think celebrity style entourages are fun, or that most need $100 or $150 MUA services. The bride, is different.

I've only been to weddings where bridesmaids pay for hair and makeup themselves.

No I think the norm is they pay for their own HMUA

I have personally never been in a wedding where I had to pay for my own hair and makeup as a bridesmaid (except for one micro-wedding where only the bride got hers done), but then again, I've never been in a wedding with as many as 15 bridesmaids! As the others have explained, if hair and makeup are optional and you don't care if they choose to do their own, then you're not obligated to pay for them.

You are only expected to pay for everyone if you require a certain look and/or that they use services you're providing