The $$$ of a valve adjustment varies dependent on your mechanical ability. If you're not mechanically inclined, it will cost you whatever a garage or stealership decides to charge you (YMMV). If you are mechanically inclined, it might cost you
1. Set of feeler gauges $5
2. Valve cover sealant (re-use your gasket if it's not leaking) $5
3. Haynes manual for step-by-step instruction and specifications $15
Most 5g Honda ownerage manuals say to have them adjusted every 15k miles. I think that's too often. Maybe check them that often, but I doubt they'd go out of spec that fast.
Tight valves kill motors, so you'd better be comfortable with feeler gauges, and know exactly how they work. You want to do this on a cold valvetrain, and you want the feeler gauges to very loosely drag between the valve stem and the rocker. You're better off on the higher side of the spec than the lower. For instance, the exhaust spec may be .009-.011"... set them for .010 or .011". Treat the intake valves the same. That lash is necessary for thermal expansion.
You don't need to drain ANY fluids or disconnect the battery. It takes about an hour after you... get the valve cover off, jack the front of the car up using jackstands to support it, remove the driver's side wheel so you can turn the crank manually with a socket wrench & extensions, and remove the top portion of the timing cover so you can see the cam timing marks. The rest is gravy. All you need to adjust them with is a 10mm box wrench, and a flat-head screwdriver. Again, follow your service manual for instructions. That part is the most important part of the whole procedure (following the steps in your manual, that is...). Also, don't overtighten your valve cover bolts when you're putting it back together.
The last time I ever paid for a valve adjustment, it was $180. I've never done that to myself again since because it's really easy after you've done it the first time. I'm sure you can get it cheaper in some places, but if I were a mechanic, that's about what I'd charge you for it.