Used microplate readers will save you a lot of money. Various companies sell used lab equipment.

The least expensive type of microplate reader is an absorbance-only one.

Consider whether you are satisfied to read only 96-well plates or if you also need to read 384-well plates.

Do you need to read other modalities besides absorbance (e.g. fluorescence, luminescence)?

Consider the performance characteristics you require, such as baseline noise, the ability to incubate at elevated temperature, the ability to shake the plate.

Do you want to be able to make absorbance measurements in the far-UV (below 340 nm)?

Yes 96 wells and nm below 340

I'd suggest looking for a used Spectramax 190.

We use Varioscan Lux from Thermo Scientific in our lab. Its efficiency is very good.