Do you have a menards close by? No idea on price comparison, but worth a check.
When we built ours, they had three choices, although I'm not seeing the WRC anymore on their site:
AC2 pressure treated pine
AC2 pressure treated pine, prestained CedarTone color
Western Red Cedar
The WRC is really nice and really light, but cost for our 14x16 was like $1500 for the CedarTone pine and mid-$3k range for WRC, so we ended up going with the pine (pic here
Also as mentioned, if you go with PT pine, try to plan and buy it close to when you are going to install it, and if possible, store the loose lumber out of direct sunlight. The wet PT boards may be straight when you buy them, but if left to dry for some time, there's a good chance they will warp. If you buy them and install while still partially wet, they typically hold their "straightness" as they dry out opposed to the loose lumber.
Last, as I was cost and material shopping around, this was the response from a pergola kit seller answering the question of PT pine vs. cedar:
As far as material, Cedar is an appearance grade lumber, it is rough sawn so it is kinda hairy. The nice thing is you can seal, stain or paint immediately. We do recommend repeating that process every two -three years.
Our Pine is a denser wood and is structural #1. It is very dark greenish when you receive it. It does need to be set up and installed for approximately 2-4 months to dry out at which time you can paint, stain or seal it at that time and repeat that process very 2-3 years as well.
You would not be making a poor choice if you chose Pine. It is a very nice wood. It is definitely not your Home Depot pine either, it's a #1 not a #2. It will last for years and years. I honestly prefer the pine in my opinion.
**footnote - his response on the pine is comparing what they offer, which is a higher grade #1 pine, vs the stuff you'd find at HD, which tops out at a #2. The lumber you see for our pergola is #2 PT pine from menards.