Don't be too strict!
A good compromise seen in most modern weddings is just allowing bridesmaids to shop for a dress in a specific shade and length. Matching dresses are passé anyway. As a bride you have a hundred of other things to worry about, so don't nitpick on the attire. Send them a few ideas for inspiration but stop there. Trust that they would choose a style that's most flattering for them.
Shop Together and get their Opinions
If you and your bridesmaids are all living in the same city, it's definitely more fun to shop for bridesmaid's dresses together. Make a day out of it and try to visit as many bridal showrooms as you can. Be sure to allow your bridesmaids the freedom to pick out their preferred styles, because they'll be the ones stuck with the dress after the wedding. Another plus if you shop together is that you can go for a bulk discount too!
If You're Getting It Tailored Consider Classic Styles
Having tailored made dresses can actually be a good solution if you're on the looking for affordable bridesmaid dresses. This is also a guarantee that all dresses will be made in the same fabric, and will fit the bridesmaids to a tee.
However, despite the fact that you now have more control over the dresses, make sure to get input from your bridesmaids too, always remember that they know what's best when it comes to their body types. Avoid insisting on matching dresses for everyone, because surely not everybody looks good in that sweetheart cut that you're obsessing over.
Allow for Removable Embellishments or Separates
There are certain details that render bridesmaid dresses unusable. Excessive beading and applique on a gown will definitely doom a dress into one time use. As a favor to your bridesmaids, keep the cut classic and the details minimal, so they can wear the dress on other occasions too.
If you are adamant about your intricate beadwork, consider making all embellishments removable. A good option is also to have a separate bodice and a skirt instead of a full on dress.