I hope the distribution things are all equal now. I'm not sure, but they didn't seem equal last time.
Last round, I got 3 Reshiram, 2 Pikachu, 2 Pignite, and a Snivy. I had to trade at my League to get the others.
My suggestion for that is going to McDonald's at least twice a week. They typically follow a pattern of two different toys a week and sometimes they'll start with the next two at the end of a week if they run out of the previous two early.
That and if you have a lot of McD's in your area, try visiting most or all of your surrounding locations. Sometimes different locations have different toys depending on their schedules.
If we purchase these separately without the meal, is it cheaper?
Yes. The toys range from $1-2 depending on the location, but most of the ones I've been to sell them for $1.50. A Happy Meal costs around $3 so if you want to save some money and not have a ton of McD's food in your fridge for several weeks I highly recommend getting the toys separately.
As a bonus, if you're looking for all the cards, don't be afraid to get duplicate toys even if they have different cards.
Oh, and try your best to not go during peak lunch and dinner hours unless you want to wait longer and annoy the people behind you in line.
Trust me, I've been collecting all the Pokemon Happy Meal toys since 2011. I know their patterns like the back of my hand.