Cost of tourist visa or is it legal for non -visa entry with a Tourist agency from Honkong?

IS IT TRUE -
1 . We can go with a Tour group from Hong Kong to Shenzhen free transit for 72 hours
2. We can go with a Tour group from Honkong to Guangzhou free transit for 72 hours?

We're hoping to be in HonKong for 4 days, then go to Shenzhen and Guangzhou for shopping and sight-seeing. We don't need a single entry one, just a tourist L or isis visa-free if we go with a tourist agency? I'm also hoping to be able to fly back to London by Qatar airlines from Guangzhou.

If we do need to get a tourist L, how mcc does it cost per person please ?

Thank you.