The reward of 'Umra is according to hardship
حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، حَدَّثَنَا ابْنُ عَوْنٍ، عَنِ الْقَاسِمِ بْنِ مُحَمَّدٍ، وَعَنِ ابْنِ عَوْنٍ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، قَالاَ قَالَتْ عَائِشَةُ ـ رضى الله عنها ـ يَا رَسُولَ اللَّهِ يَصْدُرُ النَّاسُ بِنُسُكَيْنِ وَأَصْدُرُ بِنُسُكٍ فَقِيلَ لَهَا " انْتَظِرِي، فَإِذَا طَهُرْتِ فَاخْرُجِي إِلَى التَّنْعِيمِ، فَأَهِلِّي ثُمَّ ائْتِينَا بِمَكَانِ كَذَا، وَلَكِنَّهَا عَلَى قَدْرِ نَفَقَتِكِ، أَوْ نَصَبِكِ ".
Narrated Al-Aswad: That `Aisha said, "O Allah's Messenger! The people are returning after performing the two Nusuks (i.e. Hajj and `Umra) but I am returning with one only?" He said, "Wait till you become clean from your menses and then go to at-Tan`im, assume Ihram (and after performing `Umra) join us at such-andsuch a place. But it (i.e. the reward if `Umra) is according to your expenses or the hardship (which you will undergo while performing it).