Before hiring a SEO professional it is advised that you gather knowledge on your own first.
SEO is not that tough and before investing money you should be aware of the latest in’s and out’s of SEO field.
There are many good books and plenty of web resources namely
-Search engine journal
-Search engine watch
-Problogger
-Wikihow
-SEOMOZ
Try this SEO starter guide
http://static.googleusercontent.com/...rter-guide.pdf
http://domainfest.com/files/Domainfe...Ogadget_v2.pdf
Don’t lose heart as its part of the game. With a limited budget it is advised you go for organic SEO.