Walk me through as a beginner

I  just purchased a house and want to start rainwater catchment. Walk me through where to find a rain barrel (they are so small and expensive at box stores- nothing in our area on FB or Craigslist), and the easiest way to begin, including installing gutters.
Links and videos welcome.

Hi Angel,
I have not installed a catchment system before, so I can't answer specifics, but two things come to mind.

First, what climate are you in? Does it freeze in your area? This will affect the advice given.

Second, measure your house/roof to get an idea of how much water you will get at one time. A way to estimate your roof size is to take 1.5 times the size of your square footage. So for a 20 by 30 house (600sqft), your roof is probably in the range of 900sqft. Watercache.com gives a formula of (sqft of roof area x precipitation amount x .623) to get gallons. Lets say you get 1 inch of rain on that 900sqft roof. If you captured all of it, you would have 587 gallons of water. It goes to show how unrealistic those 30 gallon rainwater barrels are :). Lastly look at the average rainfall for your area to get an idea of how much storage you may need.

Important questions first.  How much water do you want, how big is the surface area of your roof, and what's your rainfall like?

Answers are far different from Ohio to Arizona.  When you get rain is as important as to how much rain you get.  In my area, there is no rain at all from May till October, so I would have to capture and store a very large amount of water to get me though the dry season.

If you want something in the 50 gallon range, look at local food manufacturing plants and see if any have bulk food-grade containers left-over.  You might get plastic 50 gallon barrels for free, or maybe a small fee.

If you want to go larger, than take a look at your local Home Depot.  There you can get irrigation tanks in the 250-5000 gallon range.  Up to 500 gallons could be thrown on the back of your truck and brought home yourself.

5000 gallons is the largest size that typically can be installed without special permitting.

Others have given you some tidbits to get you started.

How much water do you want to collect and why?

The water tank we bought was from Tractor Supply.

They are big so having a way to get the tank home would be the first consideration.

We had a 8ft wide trailer and it was no fun trying to get that tank home from about 100 miles away.

If that is not a problem then getting gutters installed on the house would be next.

What kind of roof does your house have?  Would that kind of roof be good for drinking water or water for a garden?

When we had our homestead we started with a simple rain barrel and gutters.

Once you answer the question other folks have asked then it will be easier for some of our experts to help you out.

Colorado for instance only allows a person to store 110 gallons of rainwater, because reasons. Check to make sure it's legal where you are, or plan to be sneaky about it. https://www.worldwaterreserve.com/rainwater-harvesting/is-it-illegal-to-collect-rainwater/

I'm using a neighbor's fiberglass dingy for rainwater. It was catching it anyway so I cleaned it and floated styrofoam egg cartons all over the top to deter sunlight and added a further fabric strainer to keep our mosquitoes.

Yeah, the neighbor is OK with it so far.

The trick is to extend the surface area that drains into it, to ensure adequate collection in the drier months.

Have a look at my signature and follow the link.
Have you research the Permies site yet?
Rain barrels IMO are useless you need a water tank.
What are you calling expensive, a satisfactory sized tank would be at least 5000L to get the benefit of volume that allows;
- settlement of fines
- oxygenising of the static water
Done properly you will not require additional filtration systems which in some cases add bacteria to water.

I had a look at the https://www.arcsa.org/ site, talk about jumping on the bandwagon!
But if it works ok.
The American Rainwater Catchment Systems Association (ARCSA)
ARCSA’s Mission Statement
To provide resources and information on rainwater and stormwater collection to promote the advancement of rainwater conservation and to work with government at all levels in promoting rainwater and stormwater management.