Only 14 of the 34 subjects are available as paper based exams, here's the list from DANTES:
CLEP GENERALS
English Composition without essay
Social Science & History
Natural Sciences
Humanities
College Mathematics
CLEP SUBJECTS
Analyzing & Interpreting Literature*
College Algebra
Freshman College Composition*
Information Systems
Introductory Psychology
Introductory Sociology
Principles of Management
U.S. History I
U.S. History II
*Optional essay is available if required by the college or university.
NOTE: The CLEP General “English Composition with Essay” test is not available as a paper-based test and must be taken at a national test center as a computer-based examination.
COLLEGE LEVEL EXAMINATION PROGRAM (CLEP)
I don't think they are different in terms of difficulty, they are certainly more expensive ($120 vs $65+proctoring fee for the online version). The other difference (which was the thing with DSST exams as well) is the waiting game: a few weeks before the results come back vs instant gratification with the online version. But I guess if you don't have the online option, it's much better than nothing.
Paper based CLEPs used to be available as a service at the educational section of American consulates/embassies (many of which closed down to the public because of terrorist threats). If you'd contact the one in your area, they might be able to help you.
If you're taking the online version, you can either pay online while registering for the exam on the spot (right before taking the exam) or possibly pay the testing center in cash and they'd handle the payment (they do that either by using a pre-paid voucher or using a designated credit card), it all depends on the testing center's policies.