My current chain is x9, but it's expensive in eBay. Can I use any 9 speed chain like on this page?
AFAIK any 9speed chain made for dérailleur should fit (single speed and hub gear chains are different)
9 speed chains are more expensive, they are thinner and not as common - so fewer cheap brands bother to make them, or stores to stock them
BUT - the chain is an important part of the bike, a poor quality chain will stick, jump and wear the rear cassette teeth more quickly. You might not want to buy the very cheapest brand you can find.