All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Hajj is obligatory on a Muslim who is capable of performing it. This is supported by the verse (which means): {And [due] to Allaah from the people is a pilgrimage to the House - for whoever is able to find thereto a way}[Quran 3:97]
Capability means having money that enables a person to pay the expenses of Hajj provided that it is in surplus to his necessary needs, like residence, and life expenditures.
As for having children, there is no doubt that it is one of the most important needs in a person's life but it does not reach the degree of necessity. Hence, you have to give priority to performing Hajj over the IVF which you said is very costly.
We would like to point out that the costs of Hajj vary according to the used means of transportation, accommodation services in the sacred cities and so on. If you choose a cheaper Hajj package, you may minimize its costs in a way which saves some money that may help you with the IVF procedure.
We ask Allaah The Almighty to Assist you in realizing all your aims and Make reproduction easy for you.
Allaah Knows best.