I use apex_util.string_to_table to parse strings, but you can use a different parser if you wish. Then you can insert the data as in this example:
declare
myString varchar2(2000) :='0.75, 0.64, 0.56, 0.45';
myAmount varchar2(2000) :='0.25, 0.5, 0.65, 0.8';
v_array1 apex_application_global.vc_arr2;
v_array2 apex_application_global.vc_arr2;
begin
v_array1 := apex_util.string_to_table(myString, ', ');
v_array2 := apex_util.string_to_table(myAmount, ', ');
forall i in 1..v_array1.count
insert into mytable (a, b) values (v_array1(i), v_array2(i));
end;
Apex_util is available from Oracle 10G onwards. Prior to this it was called htmldb_util and was not installed by default. If you can't use that you could use the string parser I wrote many years ago and posted here.