Consider buying doors and using the cabinet boxes. If you get MDF (compressed fiber board) they are cheap and paint nicely. Thermofoil is a big hassel to paint and even when you do it right, sometimes it still doesn't work. Get the hinge holes routed to save a heap of trouble. Spray primer and then paint. Check these out.

Here is a link that might be useful: paintable doors

It's really difficult to paint plastic and have it stick. First, you need to determine if it's thermofoil or melamine. Thermofoil is thicker thqn melamine and slightly stretchy, so it's difficult to sand. Melamine is harder and more rigid, and can scuff readily with sandpaper. If you have flat slab cabinets, they're probably melamine, and if they have some profile to them, they are probably thermofoil.

Thermofoil will need to be wiped down with a chemical deglosser that slightly melts it surface. That will allow the primer to bond with it. Melamine will need to be scuff sanded thouroughly. You need an alkyld primer, and do two coats, allowing it to thouroughly dry between coats. Then you can choose any color of latex enamel for a top coat that you want. That paint job will get you by for a while, but it won't really hold up to the long term. It's also a lot of work. It's up to you if you want to go through all of that for a limited benefit, but I'd personally save my effort and money towards a more thourough redo. If they were wood, it'd be another story, but painted plastic, well...... I wouldn't go there.