How much you spend on your bridesmaids gifts will largely depend on your wedding budget or how much you can afford. There are a few different schools of thought about how much to spend.
Do keep in mind, is how much your bridal party is are shelling out big money for your big day. For example, they may be paying for hotel rooms, buying their own dresses, shoes, hair, nails, and makeup for the wedding. Your bridesmaids will also be spending a good amount of money on your bridal shower and bachlorette party as well. Not to mention a bridal shower gift and wedding gift. Think about all the expenses they will need to pay for, and decide what an appropriate amount for a thank you gift should be. While you're not required to buy something that equals how much they've spent, but the amount you do spend, should convey a sincere gratitude for their dedication.
Naturally, you’ll want to give more to your maid of honor, as she is a key figure in the wedding party and has a great deal of responsibility. Her job to act as point person for pre-wedding events, coordinating and organizing the pre-wedding parties, and more. She's also the most important person of your friends or relatives, so consider spending a little extra on her for the extra effort and time she's put out for your wedding.
The rehearsal dinner is a great opportunity to present these gifts to your bridal party and thank them for their support and help. Other couples may give the gifts the morning-of the wedding, if they have time, as everyone is getting ready. Regardless of where you present your gifts, just make sure to convey how thankful you are for your bridesmaids and how you couldn't have made the wedding day everything it is, without them by your side.