First of all, you don't need the -r flag which is (from man cp):
-R, -r, --recursive
copy directories recursively
That is only useful when copying entire directories and their contents. Then, whenever your file names contain strange characters, you need to either escape them or protect them with single quotes as the other answers have already suggested:
cp '$somefile.class' /folder2
cp \$somefile.class /folder2
Alternatively, you can use the shell's glob expansion feature to copy the file:
cp ?somefile.class /folder2
cp *somefile.class /folder2
The ? matches "any single character" and * matches "0 or more characters". So, using these globs will allow you to copy the target file without worrying about the name. However, bear in mind that you should use this carefully and make sure that the globs only match the file you want to copy. For example, the ones I used would also match Lsomefile.class.