I am new to casting myself. I may be wrong with what I write and I hope others will chime in.
Are you looking for cheap as possible with low production or faster but a little more expensive?
You can go cheap and buy dipper, furnace, Lee tumble lube mold, and a lee lube and sizer kit.
If you want some more speed get a bottom pour furnace. You can buy a good Lee for about $60 before shipping or more expensive furnaces. I love the RCBS but it cost over $300.
Lee molds are a great place to start. When you gain experience the 6 gang molds are a pleasure to use. You can find Lyman molds used for $45 shipped and new lee 6 gang molds for $35 or so plus $12 handles.
I bought a Lyman 45 sizer from Castboolits.com or THR for $45. Sizing dies are $9-$18 depending on new versus used. Top Punches are $8 or so.
Ask at your local tire shop for wheel weights. Typically a 5 gallon bucket of wheelweights for $20 - $25. After processing (smelting out inpurities, removing stems, and steel clips) you will yield abou 80-100 pounds of lead good for casting. At 7000 grains per 1 pound of lead that's 700,000 grains or 4400 bullets for your .357 if you shoot 158 Grain bullets.
For smelting, you will need a cast iron dutch oven, about $25 and the base of a turkey fryer. You will heat the wheelweights until they just melt and use a slotted spon to skim off the steel clips. Remove the tire stems before heating. If you have a thermometer, heat the smelt to 700 and skim. As the temperature increase, zinc can be melted into the solution for disastrous results. After the clips are removed, pour in a small amount of motor oil, toilet ring wax, candle wax, or sawdust. Stir this in and skim off the black that forms. Use a ladel to pour the lead into Cast iron or steel muffin tins (that have rust or a graphite spray on the sides) and you have ingots.
Use these ingots in your furnace and flux again before casting.
I think you can get into casting for $200 and your payback is almost instantaneous. $200 for materials, $25 for wheel weights, propane. Your first 100 pounds of wheel weights make over 4000 bullets. What is the current cost of 4000 bullets? Materials are paid for!
Hope this helps. Feel free to PM me with questions.