Well I think you should always train with RS gold slayer it shouldn't take that long to build up to 70 all in all, maybe several days, depending upon how long you play each day.
An excellent set-up for slayer which is fairly cheap is to put on a Slayer Helm, or Neitznot (sp?) Helm until you acquire the slayer helm Amulet of Glory, Fighter Torso (can easily be acquired within a few hours) Platelegs of Torag's or Verac's Plateskirt , if you'll use prayer for your quests as it offers prayer bonus, Whip /Dragon Scimitar Dragon Defender, and Dragon Boots and Obsidian Cape (unless you already have the skillcape or firecape).
Keep in mind that this is just an advice for equipment and you are able to switch things to a different level. For instance, you could replace your defender with an Obsidian shield when you believe you require the extra defensive boost, and cheap OSRS GP you can always make use of dragon platelegs if you do not want to fix the armor on your barrow, as it breaks down in combat.