Man,
I am gonna make it short, and simple for you. There is not such thing like "cheap and relevant links", trust me... I am assuming you want quality links since you said relevant... Ive worked on massive link building campaigns, and cheap/spamy links only help Google to detect you and devalue all your quality links and possinluy deindex your site..
Did you do top 200 dirs submission? If not, do them.
Did you do 100+ article distribution using services like isnare? If not, do that?
Did you do 5 press releases? If not, do that
These all cheap and WORKS very well, indeed they will costs you at least 5k, and thats cheap. You should do those in a period of 6 months...
But before you build links, ask one question: Does my site worth the time of link building? Is it possible for me to rank? If you are trying to rank for "car insurance", do not waste your time... It took us 3 years to rank for keyword like that..
Good luck!