Breeding is a fairly expensive process. There is no way around the fact you are going to have to spend money. However, the first spawn is always going to be the most expensive because you have to purchase everything from scratch. Subsequent spawns will be cheaper because you already have the equipment and (usually) live food cultures on hand.
Purchasing tanks and heaters second-hand may be the cheaper option. However, there is no guarantee that the tanks are watertight and any equipment such as air pumps or heaters aren't going to be faulty.
Basically your best bet would be to shop around. Visit as many online stores as you can and compare prices for things like sponge filters, jars, heaters etc. as these are usually much cheaper than in store. Starter food cultures can usually be sourced extremely cheaply from other hobbyists and will generally be ready for harvest in a couple of weeks.