Are you looking to buy tools just for this one site you're working on? Are you investing in tools to help you create new IM projects/campaigns? Just a couple of questions...
How about your current website. Are you looking to make a purchase on something that will immediately help in ranking your pages of this? (That is what it sounds like from your OP but a little clarification will help provide you with better answers.)
The correct answer is D) All of the above.
But this doesn't really help you, now does it?
My advice is let us know what type of IM you have going (just the basics, not your niche or methods...keep those to yourself) so a clearer picture can be drawn.
Your question has been asked and answered many times on this forum...only differently like "I have $400 to spend" or "I have $1000 to spend". Also, many choose not to spend a dime more that a domain and hosting.
Help us to better help you by providing a bit more information about you and your campaign. Important for us fellow members to know are things such as whether you are a good article writer or not, if you know about on-page SEO, if you know about off-page SEO, etc. Also, how is your site doing in rankings and for traffic?
Maybe advice on your next step should precede a recommendation on what to buy.
You have one of the most versatile tools already with SB. For TA, are you focusing on Twitter marketing or just using TA for growing healthy Twitter accounts?
Looking forward to hearing a bit more info. If you would rather, feel free to PM me but I feel others in this thread are interested in this same topic.