Final answer:
Crack cocaine is the alternative to cocaine used because it is cheaper. Methamphetamine is also a cheaper stimulant alternative, but the mention of broken lumps of the free base in the question refers specifically to crack cocaine.
Step-by-step explanation:
The alternative to cocaine that is used because it is cheaper is d) Crack cocaine. However, it's important to note that other substances, like methamphetamine, are also used as cheaper alternatives. Methamphetamine, known as crystal meth in its smokable form, is highly addictive and can be made from readily available ingredients, making it an inexpensive but dangerous alternative. Crack cocaine is a form of cocaine that comes in broken lumps of the free base, known for its lower purity level which leads to its lower cost compared to cocaine hydrochloride. This form of cocaine can be particularly destructive due to its high potential for addiction and the intensified peak effects that encourage repeated use, often leading to physical and psychological harm.