* Cost of Repair: Get at least three quotes from reputable mechanics. A head gasket repair on a relatively simple engine *could* be relatively inexpensive, but it depends on labor rates in your area and any additional damage found during the repair (like warped heads, etc.). It's almost certainly going to cost more than just replacing the head gasket itself. Expect it to be at least a few hundred dollars, possibly more.
* Vehicle's Overall Condition: A 1999 Metro is a very old car. Is the rest of the car in good condition? Are there other significant maintenance needs looming? If the car is generally well-maintained *except* for the head gasket, it might be worth fixing. However, if the car needs tires, brakes, suspension work, etc. *in addition* to the head gasket, the cumulative repair costs could easily exceed the car's value.
* Value of the Vehicle: What is the car worth? You can check sites like Kelley Blue Book (KBB) or Edmunds to get an idea. If the repair cost approaches or exceeds the car's value, it's likely not worth fixing.
* Your Mechanical Skills: If you have the mechanical skills and tools, you might be able to save money by doing the repair yourself. However, this is a moderately complex repair and mistakes can lead to further damage.
In short: For a 1999 Metro, a head gasket repair is a significant undertaking. Unless the car is otherwise in excellent condition and the repair cost is substantially less than the car's value, it's probably *not* worth the investment. You might be better off using the money to purchase a more reliable used car. Before committing to the repair, carefully weigh the cost of repair against the car's value and overall condition.
