There is very little point in starting a Linux club if your kids do not have computers on which to try Linux. Luckily, most versions of Linux run well on older machines, so it is not necessary to get expensive new computers.
Where you get your computers will depend on what resources are available in your area and how many you need. Here are a few things that worked for us:
Ask people you know for used computers. Most people at some point will upgrade their own personal computer and will need a place for the old one to go. Once you have it, either install Linux on it yourself or teach your students to do it. Don't forget: if you are doing your Linux club under the auspices of a non-profit (such as a school), people who give you computers can deduct those donations from their taxes.
Your school’s IT department. Just as individuals upgrade computers from time to time, so do schools. If your school has recently changed out some of its hardware, ask for some of the recently retired stuff. You might even be doing them a favor by taking the computers off of their hands, as they would probably have to pay to have the old computers recycled.
In Minnesota, we have the Minnesota Surplus Exchange, which is where the state sells off surplus used stuff like computers to qualified agencies, such as schools. Computers from them come wiped clean, with no operating system. (For the Surplus Exchange a school must be registered as a qualified agency, and only people your school chooses to be authorized purchase agents can go in and buy. However, the Exchange also has online auctions available to the general public.)
Phone: Admin Surplus Services 651-639-4022
Auction website: https://www.minnbid.org/Mobile/Auction
Local companies, corporations, and nonprofits retire and replace computers regularly, and they are often open to donating their computers so that they can be used again. Try contacting some of them, particularly through your acquaintances that work there. Again, these donations are tax-deductible. At Aspen Academy, local companies and non-profits became our biggest source of computers, ultimately enabling us to provide computers for over 300 students during Distance Learning.
Online appeals for donations over social media and news media. When Minnesota schools had to close and convert to Distance Learning due to COVID-19, we put multiple messages out over Facebook, Twitter, Youtube, and local news media asking for computer donations. This put us in touch with both individuals and groups who gave us computers.
Thrift stores can be worth a look, especially if they have taken on the challenge of recycling computers for sale at their stores. One such store is the St. Vincent de Paul Thrift Store in Minneapolis. They sell computers running both Windows and Linux (Windows machines cost a little more).
Minnesota Computers for Schools is a program run through the Minnesota Department of Corrections, in which inmates learn job skills by learning to recycle computers. These computers are then sold to Minnesota schools at a discount. Computers can be purchased with Windows or with no operating system at all, and they often have good deals.
Free Geek is a non-profit that recycles computers with Linux to help close the Digital Divide and reduce e-waste. There are several local Free Geek organizations around the country, and most have stores that sell computers cheaply, as well as grant programs to get computers for free. Here is the information for the Minnesota chapter, Free Geek Twin Cities:
Tech Discounts is another computer recycling program that has computers available for sale. Something noteworthy about Tech Discounts is they provide jobs and job training to individuals with barriers to employment. Computers here can be purchased with or without the operating system, and schools can be eligible for discounts. They have two locations: Golden Valley and Bloomington.
Ebay has lots of computers available cheaply and ready for a fresh install of your favorite flavor of Linux. A Linux educator colleague of mine, Phil Shapiro, in the Washington, DC area has a YouTube video where he explains and shows the $20 laptop he bought on eBay. This laptop surfs the web nicely with Linux. https://www.youtube.com/watch?v=UZiN6nm-PUU. Please keep in mind that when buying a computer on Ebay you also have to deal with shipping charges.
All of these sources are helpful for both desktop and laptop computers. While all of these examples (except Ebay) are from Minnesota, similar programs and places exist in most other states. All of these sources of computers have worked for us. They can work for you, too.