Is it theoretical CS as in "CS topics that are more theoretical" (NLP? AI? Search engines? Software engineering?), or as in "Theoretical CS" (the mathematical subdisciplines: combinatorics, type theory, lambda calculus, etc.)?
In any case you first need to investigate what is interesting to you, free resources are far from rare and you can probably build yourself a decent curriculum from MIT OCW, Coursera, Udacity and similar websites which you can then study at your own pace with videos and books. If finding a job is not your concern I wouldn't advise putting yourself into debt. See http://www.saylor.org/majors/computer-science/ for an example of curriculum.
In any case you first need to investigate what is interesting to you, free resources are far from rare and you can probably build yourself a decent curriculum from MIT OCW, Coursera, Udacity and similar websites which you can then study at your own pace with videos and books. If finding a job is not your concern I wouldn't advise putting yourself into debt. See http://www.saylor.org/majors/computer-science/ for an example of curriculum.