iPad batteries typically last for many years in regular use. A swollen battery is faulty battery - and not simply a battery that has reached the end of its usable life.
Apple quotes its iPad batteries to retain at least 80% of its original capacity after 1000 full charge cycles - a “full cycle” being any combination of charging that sums to 100% (e.g., 50 + 20 + 15 + 15 = 100%).
If battery service is not offered by an Apple Authorised Service Provider (AASP) in your country, your options are somewhat limited. If battery replacement cost is broadly equivalent to replacement with a new model iPad (potentially with better technical specifications), replacement of the iPad is perhaps the most obvious and advantageous option.