How many IUIs before going to IVF?

I’m just curious, how many failed IUIs do you think is enough, before moving on to IVF?

I’m 40 and have been naturally TTC for almost 8 years now. I’ve been through a couple of IUIs and they failed. IVF is so dang expensive so we ignored our first clinics suggestion and went to another clinic for the IUIs.

Right now I’m feeling foolish and also like I’m running out of time. I really don’t feel done having kids, like my family isn’t complete. My husband wants me to move on, but will semi-happily keep going if I want to keep on this path. I’m starting to feel guilty about not letting this go.

So. Many. Mixed. Emotions.

I guess I’m just looking for some advice.