All depends on which country you are in,
If Australia - (Myself!) i'd be more than happy to give you heaps of contacts for whatever state your'e in! (since soap suppliers are notoriously difficult to track here lol)
If USA - bramble berry is probably the best (not saying this just because they own this blog! haha) but because they have a huge range of sopamaking supplies and pretty much anything soap
With other countries - just try looking up local soap suppliers, or even just go to the local supermarket, i never went the melt and pour route since for me it seemed too limited - just went straight into CP Soap (though did do a soap making class first which was 100% worth the cost and time)
But Anyway for melt and pour soap i'm pretty sure from memory looking it up you can get 1-2kg melt and pour soap bases for around $20 - $30 with free shipping, then all you really need is a soap pot and a few moulds, with more equipment and materials can do more - thermometer, spatula, soap colours, Essential Oils or Soap/skin safe Fragrance oils, etc....
Anyway have fun and good luck!