What classical guitar strings for my Yamaha Apex-5NA?

Lemme get this straight - you change them every other year and you don't want to "break the bank" on strings?

The economy must be tougher than I thought. If you change strings every couple of years, the most expensive ones on the market work out to about a nickel a day. Anyway...

1. There are no "best" strings. What you like, someone else will hate. It's all about your playing style and the tone you're after.

2. The more tension, the more sustain you get - and the more stress you put on the guitar. The less tension, the easier it is to fret - and the more likely you are to get some buzzing. If you're changing strings every couple of years, stay away from the two extremes (light/extra hard) and get a medium, medium-hard, or hard set.

3. Coated classical strings: the trebles are nylon (or on high-end strings, carbon fiber), which don't need coating - they don't rust/tarnish, so they last longer than the basses. Bass strings are usually silver wound - although some sets use bronze, titanium, or other wraps - and they'll last a little longer if they're coated. But since you're not playing very often, it's probably not going to make a huge difference - as long as you wash your hands before you play :)

4. D'addario makes several types of classical strings; we carry their Pro-Arte line at our school. They're good strings for most players. They do make an EXP coated classical set, which they claim lasts 3-4 times longer than other nylon strings (but I very much doubt you'd get 8 years out of them!). I haven't tried them. But just in case your question is literal: EXP acoustic strings would be a bad choice; you want nylon strings.