Depends on what you mean be a valve leak?
Burnt valve or seat?
Worn guide not landing the valve concentrically on the seat?
Spriings not strong enough to keep the valve tight on the seat?
Constant overrevving to where the springs or guides become damaged?
A common thread with low end import heads is guide wear and inadequate springs. To a big extent guide wear is insufficient cleaning prior to assembly and a lack of stem lubrication. Assembled head’s tend to use springs inadequate to the loads put on them.
Basically you need a competent shop to tear them down and inspect for root cause issues.
Anymore a 1000 bucks doesn’t buy much, the imports have become pretty expensive thanks to high tariffs the previous president had levied and the current one hasn’t reduced. Probably the best bang for your buck on import head’s is the FloTec, these are essentially an aluminum copy of the L31 Vortec. For domestics Edelbrock and Patriot have some in your cost category. I think the Patriot has a better combustion chamber. The Edelbrock chambers are simpler and tend to be bigger so you have to watch where your compression is going.
For assembled head’s no matter who’s, I disassemble them and clean them really well especially in the guides, then plug the guides and fill them with oil to set for a few days before draining them then apply assembly lube with a brush in the guide and to the stem to insure the guide is lubed end to end as with modern tight stem seals the guides get damn little oil especially the exhaust side that sees pressure that tends to blow the lube back up the stem, not to mention temperatures that burn off the oil. High lift cams are a big contributor as more of the stem is exposed to the high heat. In many respects using an umbrella rather than a positive seal on the exhaust side works better as they allow more oil splash to get to the valve stem, talking exhaust side. The intake valve runs a lot cooler and sees vacuum which induces some oil to enter into the guide past the seal so these generally have less problems than the exhaust side.
You want to be sure the valves you use have hard or industrial chromed stems as this wears well with minimal lubrication. Most valve do have this, but be sure yours do.
Bogie