There is a Hadith that is often recited during fund raisers:
Abu Hurairah narrated that the Messenger of Allah (ﷺ) said:
“Take on only as much as you can do of good deeds, for the best of
deeds is that which is done consistently, even if it is little.”
حَدَّثَنَا الْعَبَّاسُ بْنُ عُثْمَانَ الدِّمَشْقِيُّ، حَدَّثَنَا
الْوَلِيدُ بْنُ مُسْلِمٍ، حَدَّثَنَا ابْنُ لَهِيعَةَ، حَدَّثَنَا
عَبْدُ الرَّحْمَنِ الأَعْرَجُ، سَمِعْتُ أَبَا هُرَيْرَةَ، يَقُولُ
قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ : " اكْلَفُوا مِنَ
الْعَمَلِ مَا تُطِيقُونَ فَإِنَّ خَيْرَ الْعَمَلِ أَدْوَمُهُ وَإِنْ
قَلَّ " . Grade : Sahih (Darussalam)
English reference : Vol. 5, Book 37, Hadith 4240 Arabic reference :
Book 37, Hadith 4381
If spending a little allows you to consistently do Sadaqah for helping others it is more better than to spent irregularly on Sadaqah.
One of the local Imams explained to me this is so that we remember Allah more often which leads to us doing more good deeds and avoiding sins. Also a lot of more people tend to benefit from your Sadaqah this way.
Also as pointed out by Saif in a comment to your question, it is not the amount but the intention that matters most. Dont be stingy but also dont spend overtly that your family gets affected .