A heat lamp and reflector socket with a spring clamp may be purchased on-line for as little as $26. The amount of time required to dry samples depends on many things including the wetness of the initial sample, the soil characteristics, the relative humidity, and the temperature to which the sample is heated. GLOBE protocols specify that samples are not to be heated above 105o C. In using a heat lamp, the temperature to which the sample is heated depends on the wattage of the bulb and the distance between the heat lamp and the sample bag.
I have tried drying a sample using this equipment. My bulb was a 250 w heat lamp. This experience has led me to make the following comments. After two days, I measured the temperature of the surface of the sample using an IR thermometer. It was just under 50o C. The lamp could have been mounted closer to the sample in order to achieve a higher temperature and I could have used the IR thermometer to check that the sample was not overheated. Reducing the drying time is desirable, particularly when school safety concerns dictate that the lamp be turned off over night. Another point is that the lamp be securely mounted using the reflectors spring clamp.
Note that sample temperature may be measured by inserting a thermometer into the soil sample. The surface temperature of the sample as measured using an IR thermometer will likely rise as the moisture in the sample is evaporated.