I need marraige advice or opinions

First just want to say husband and i have never fought over money and were not fighting now im waiting for a response. My mom asked me if we could help pitch in momey to buy my sister who is in military training, a plane ticket home for next month its $800. I told her maybe i can give 100 but id talk to hubby about it first. They btw have a great relationship w my husband. So i brought it up to my husband he didnt say no but he started to say all the bills we have coming up and whatnot but i know what bills we have and in all honesty of a $700 paycheck we need 140 for bills. And thats all we need from this paycheck we already have food and gass everything is up to date i know i do our bills. So he hasnt said no but i can see he doesnt really want to say yes. So im kind of upset because we have given his family waaaay more money in several instances and ive never minded or said anything and im tempted to bring all that up i mean in 2 and a half years married weve given his family maybe 5000 and my family none. So this is the first time and its just 100. I want to bring it all up but i feel like its not the right way to go about this like saying weve done all this for yours so you need to do this for mine. Uhh idk should i just not say anything or what