Not sure if i can comment too well on a pure warlock, but I had a multiclassed warlock-monk-rogue (dont ask, it was trying to be a shadow assassin type), and i think if i had to redo the character it would be a pure warlock as that was the most enjoyable part of it, as a first time 5e player, id...
if the OP is still looking for a way to get into magic these days on the cheap, the commander decks (and edh format) is a good way to both get a solid deck and a great gameplay experience through a multiplayer game.
if you're just looking for an intro-style deck to play 1v1, the planeswalker...