Well, if a traditional waterside economizer system just isn't in the budget, there could be another option. I like to refer to it as the "poor man's economizer" or PME. Basically, the PME uses AHU chilled water coils to reduce the chilled water temperature in the loop, essentially using the chilled water coil as a "dry cooler" to provide free cooling. And when the AHU requires preheat, there can be additional cost savings associated with preheat reduction.
Figure 3 illustrates one method to achieve this with some example values. Essentially, it's just a matter of adding some control valves, sensors, and programming. In the economizer cooling mode, the 60°F chilled water return bypasses the normal source of chilled water (chiller plant or purchased chilled water). The chilled water is cooled by the outside air to 45° at the AHUs, then directed to the economizer load chilled water coils. Note that the coils are then in series, so you need to make sure the pump can handle the additional head. Although the installation costs of this type of system would be much lower than that of the traditional waterside system, the operational cost savings can be comparable or even better in some cases.