It’s OK to say no because you can’t afford it. And it’s up to your discretion whether you still want to send a smaller gift or no gift at all.
if you have a different event every single weekend of the month, that gives you no time to spend a weekend doing what you want. You need to put yourself and your mental and physical wellbeing first, too!
It’s OK to say no to one because you have another one the same day or weekend. Think about which one you want to go to more and/or which one means more to you. If you have a partner, make the decision with them.