12 year old cat loseing weight and throwing up?

my cat is 12 he is a house cat rarely outside no change in food type been throwing up alot lately sometimes just liquid sometimes undigested food. i dont have enough money for a vet visit yet still saveing up he plays and sleeps and loves all the same just loseing weight these last few weeks and im really worried i dont know how to get him to eat more and to gain some weight and i have no idea why he is thowing up i figured because of the warm weather he was getting hairballs cause when he first started throwing up it had hair in it but now its all food or just liqid any ideas, tips, advice?