It is important to think over following points before deciding whether to purchase a Gantry Crane or an Over Head Crane:

• Purpose for which the crane is meant:  For example, will it be used to move expensive tools into/out of a molding machine or to load/unload steel from trucks?, indoor use/outdoor use
• Safety of the loads being lifted
• Safety of workers in handling the loads

• How often will it be used 
• How will the load need to be moved and located
• Do you foresee a possibility of shifting of crane to a new location? If "yes", then how easy is it to move the system to a new location 
• Dimensions of place where you are going to install the crane
  
• Requirements of Lifting capacity, Length of lift, and the Area of hook coverage
• Do you really need three axes of hook movement (e.g., up/down, left/right, and forward/back) or will only two be sufficient?
• Select your power options. Some smaller gantries aren’t powered in the hoist/trolley motions. Many gantry cranes aren’t powered in the gantry travel motion. It’s an expensive feature.
• Make sure to select the proper voltage.
  
•  How much money you can invest in a system

Gantry cranes are generally available in spans to 150 feet and capacities to 150 tons. Gantry cranes are often cheaper than Over Head Cranes.

However, NOT all Gantry Cranes cost less than their bridge crane counterparts. A gantry crane is a more cost-effective alternative if:

• You are currently in a leased/rented facility and do not want to make a major investment in a overhead crane runway structure.
• You may be planning to move the crane in the near future and want to take your entire investment with you.
• You require a crane system that moves loads between the interior and exterior of your building.
• You need long runway structures of over 150 feet where the runway steel and foundation costs are very high.

You should calculate the total investment (i.e. inclusive of crane cost, installation cost, cost of runway structure & foundations) while comparing various options.