Payment

Earth is invaded by shape shifting dragons. They appear in human form to not frighten the humans. They claim to be here to help humanity and cure all of diseases and improve humanity's technology. But they want payment.
Payment in the form of women, they have no females in their species. Their females were killed by war and disease. At first they take only volunteers. The women are whisked away to the aliens' world. The volunteers aren't enough. The aliens require more. The government figures to kill two birds with one stone, take women from the unemployed and give them to the dragons. Unemployment gets better and the payment is made to the dragons.
Lily worked in a hospital, had a boyfriend and had a good time. Then the aliens came. While others were touting how good they were, her life changed drastically. She worked in a hospital and when diseases were cured, she was no longer needed. No job, no money to pay her way (particularly pay for her birth control), her boyfriend dumps her.
Unemployed and unattached, Lily is selected to give to the aliens. A letter arrives ordering her to report for selection. She refuses and tries to escape. As she's climbing a mountain in the wilderness, a dragon sweeps down and snatches her.
Fighting her disbelief, she struggles, beats on the dragon. He sets down on a mountain cliff to rip her clothes from her curvy luscious body. Aroused by her resistance, the dragon mates with her in both his forms.
Lily is excited and satisfied by the sex and agrees to go with him. On his ship, he keeps her in bed having sex for days. When she wakes from the sex haze, she discovers he expects her to bear his children - lots of children.