I prepared a 1:200 dilution of red blood cells using a ~1% NaCl solution. The imaged region contains 4 nano liters of the diluted sample. This image was taken using a 40x objective.

A count is performed by counting the number of red blood cells in a few of these sections, averaging the result, and then converting back to red blood cells per microliter by multiplying times 200 (dilution) and dividing by 0.004 (sampled volume in micoliters).

For this particular sample I estimated 3.8 million red blood cells per micro liter of blood.

I tested a few different types of hemocytometer/Neubauer chambers from China and I can recommend this specific one:

There are some even cheaper alternatives but the lines are very difficult to see.