Anyone who's had an apartment painted has a story: a one-week job that lasted eight weeks, a $2,000 estimate that turned into an $8,000 bill. "Once they're in your house," says one dispirited homeowner, "they've got you by the tail." Painters who produce beautiful walls while sticking to time estimates -- and your budget -- can make the invasion a happy experience, whether you're simply freshening up the place with a coat of paint or doing a complete wall renovation. If money is no object, count on Roth Painting (305 East 46th Street; 758-2170) to spare no cost while attending to every detail. "They'll stand there for months sanding away," swoons one happy, rich customer. For a high-end job with a more midsize bill, there's Zeccodec (42 Stuyvesant Street; 254-1500). Owner Glenn Zecco claims that 98 percent of his clients (including decorators and architects) are repeat customers. And, he says, "I never approach a project by telling someone what they want to hear. I lay it on the table, and then the client can make the decision."