Hi and welcome to the forum! I battle pigweed too. Is it in your vegetable garden or flower beds? For a veggie garden, what I would suggest is to leave it fallow for a year and till it often so as to not let the pigweed go to seed. Unfortuneatly, for me that's not possible, so I just try to keep on top of them as much as possible, because if you let one plant go to seed, you'll have hundreds more later. Using round-up in a large area would also work, but it's difficult to use in a tightly packed flower bed though. On the bright side, I find that pigweed isn't terribly hard to pull out as they don't have a huge taproot like dandylions. Anyway, that's my experience with pigweed...... others may suggest alternate ideas for you too.
As for the most cost effective way to get good soil, I suppose if you get to know a local farmer who will give you well aged manure, then you're laughing! Also composting your organic waste and adding it to the soil is free. For my veggie garden, what I do is, all winter I throw out my kitchen scraps right into the garden and in the spring it gets tilled into the soil. I find that over the 9 years I've been doing this, it's helped a lot.

Good luck,
Laurie

Your best bet is to keep on top of it, the best method of control is to hoe....hoe them down before they can set seed. Try not to disturb the soil too much, otherwise you'll bring up seed to the soil surface to germinate.

Sharon

Good advice on pigweed control. This is an annual weed, fairly easy to pull and cultivating/disturbing the soil will only bring more seed to the surface to germinate. It does not deter me from using composted manure in my gardens. A case of the benefits outweighing the downside by a long shot.

It is common for manure to contain both pigweed and lambsquarter seed. Why? is a mystery to me. Both of these weeds are pioneer species....coming in on barren/disturbed soil...like in gardens. Our livestock graze on pastures and fields that do not contain any pigweed....yet the manure always has a tremendous supply of these seeds. In moments of lofty thought, I ponder this great mystery! LOL.

My current weed problem is sow thistle. I have never had this before in any of my gardens and this year it appeared by the millions. I think every bird within a hundred mile radius feasted on this seed and then came directly to my gardens to dump their load.
Sow Thistle is one bad weed. It has a tap root that can go as deep as a meter. It starts out as a little prickly rosette and, I swear, in less than a week it is a full grown plant setting and distributing its dandelion-like seed all over the place. You can't pull it because of the tap root. If you break off the root it comes back again from the root. Unusual for an annual. I am losing the battle on controlling this noxious weed despite spending countless hours digging it out. Just when I thought I was making progress against the Purslane...this awful thing shows up....sigh.
Jan

The purple stemmed weed you mention is likely lamb's quarters as Jan mentioned. It's got a more sprawling growth habit but gets big and bad fast like pigweed. It and pigweed seem to go hand in hand. I have problems with both in my gardens as well.

Jan OMG I have sow thistle problems like never before too! They are SO bad. It must be a good year for them. And I accidentally let some groundsel go to seed last year... I could complain about my weeds all day. Next year I am getting mulch if I have to drag it home in the wheelbarrow.

I live in Northern Wyoming, having moved here from the Mid
Atlantic region. One of the first things I noticed about the weeds here, including pig weed is that they seem to think that Roundup is fertilizer. The most effective killer I have found is also very inexpensive, fill a spray bottle with full strength bleach, add a bit of dish soap and spray what you want to kill. You will very quickly see it start to work. If it isn't completely effective the first time, hit it again.