This site (and its UC Davis so reliable)
lists plumeria as a 4 which means
"Dermatitis: The juice, sap, or thorns of these plants may cause a skin rash or irritation. Wash the affected area of skin with soap and water as soon as possible after contact. The rashes may be very serious and painful. Call the Poison Control Center or your doctor if symptoms appear following contact with the plants. "
So it is likely the sap caused some irritation to the digestive tract which resulted in the vomiting to get rid of it.
You may want to see if he will drink something for you to help sooth any irritation from the plant fluids or the vomiting. You might try a half cup of milk but be aware that can be a mild laxative too.
Just in case and for future reference, as cash flow is an issue, check with your local humane society to see if there is local low cost vet care, ask your vet if you can do time payments or here are some groups that might help you afford the vet bills:
American Animal Hospital Association
" Through the AAHA Helping Pets Fund, veterinary care is possible for sick or injured pets even if they have been abandoned or if their owner is experiencing financial hardship."
Angels 4 Animals
"Our services range from financial aid to complete treatment
to those pets and pet owners in need."
A credit card company for health care, including veterinary care.
"With a comprehensive range of plan options, for
treatment or procedure fees from $1 to over $25,000, we offer a plan
and a low monthly payment to fit comfortably into almost every
budget." They have a zero interest program if you pay within a certain time frame and they list the vets who work with their product.
God's Creatures Ministry
"This fund helps pay for veterinarian bills for those who need help."
"Our efforts focus on serving the elderly, the disabled, and the
"We are dedicated to insure that no
companion animal has to be euthanized simply because their caretaker
is financially challenged."
The Pet Fund
"The Pet Fund is a registered 501(c)3 nonprofit association that
provides financial assistance to owners of domestic animals who need
urgent veterinary care."
United Animal Nations
"The m ission of LifeLine is to help homeless or recently rescued
animals suffering from life-threatening conditions that require
specific and immediate emergency veterinary care. We strive to serve
Good Samaritans and rescue groups who take in sick or injured
animals. In certain cases, LifeLine can also assist senior citizens
and low-income families pay for immediate emergency veterinary care." They also keep a list of local and national help resources here