SQL & PL/SQL :: Value For Closest Or Equal Date

I have two tables e.g. test_bb and test_sub

I would like to select test_sub.price as per the below conditions. If test_bb.value_date, test_bb.vehicle matches to test_sub.value_date,test_sub.vehicle then display test_sub.price

If there is no match then as above find the closest test_sub.value_date which is less than test_bb.value_date and select corresponding test_sub.price for the same vehicle combination.

e.g.

select * from test_sub;
VEHICLE VALUE_DAT PRICE
---------- --------- ----------
10 12-APR-12 2
10 08-JAN-10 4
10 14-APR-14 6
10 06-AUG-47 8
20 24-JAN-14 10
20 20-FEB-06 12
20 18-FEB-04 14
20 28-FEB-06 16
20 22-DEC-07 19
8 rows selected.

select * from test_bb;
VEHICLE VALUE_DAT
---------- ---------
10 12-APR-12
10 10-FEB-10
20 24-JAN-14
20 22-FEB-08

Required output:
VEHICLE PRICE VALUE_DAT
---------- ---------- ---------
10 2 12-APR-12
10 4 08-JAN-10
20 10 24-JAN-14
20 19 22-DEC-07

create table test_bb(vehicle number, value_date date);

begin
insert into test_bb values(10,to_date('12-04-2012','dd-mm-yyyy'));
insert into test_bb values(10,to_date('10-02-2010','dd-mm-yyyy'));
insert into test_bb values(20,to_date('24-01-2014','dd-mm-yyyy'));
insert into test_bb values(20,to_date('22-02-2008','dd-mm-yyyy'));
end;
/

create table test_sub(vehicle number, value_date date,price number);

begin
insert into test_sub values(10,to_date('12-04-2012','dd-mm-yyyy'),2);
insert into test_sub values(10,to_date('08-01-2010','dd-mm-yyyy'),4);
insert into test_sub values(10,to_date('14-04-2014','dd-mm-yyyy'),6);
insert into test_sub values(10,to_date('06-08-1947','dd-mm-yyyy'),8);
insert into test_sub values(20,to_date('24-01-2014','dd-mm-yyyy'),10);
insert into test_sub values(20,to_date('20-02-2006','dd-mm-yyyy'),12);
insert into test_sub values(20,to_date('18-02-2004','dd-mm-yyyy'),14);
insert into test_sub values(20,to_date('28-02-2006','dd-mm-yyyy'),16);
insert into test_sub values(20,to_date('22-DEC-2007','dd-mm-yyyy'),19);
end;
/

I could write as below but I would like to know if there is a better way of doing it.

select bb.vehicle
,sub.price
,bb.value_date
from test_bb bb
,test_sub sub
where bb.vehicle=sub.vehicle
[code].........