My first reaction is that you are in Sales, yet you are being given a Marketing budget. It sounds like your company does not understand the distinction between Sales and Marketing.
What I would do with my $1K/month would depend a lot upon what corporate-wide marketing outreach programs are in place to build brand awareness, credibility, etc.
If such a program is in place, then I would focus my efforts on identifying a niche where you are already strong (you already have several accounts there) and dominating it.
If such a program is NOT in place, then that's a whole 'nother animal.