Question: I'm working with a client whose sole selling point is affordability. They sell at low margins and aim for the cheapest of demographics. 

What are some UX or design decisions I can make to make their visitors feel like they are making a bargain?

Some obvious ones are large text for prices. Perhaps strike through list prices and show discounted prices in red and so on. But are there other ways to achieve "affordability"?

Answer: 
**Without going into dark UX patterns, I'd recommend many of the techniques from <http://www.goodui.org/>**

Some specific examples would be to recommend a specific product instead of treating everything equally ([#7](http://www.goodui.org/#7)), use the anchoring effect on prices or trim the cents ([#41](http://www.goodui.org/#41), [#51](http://www.goodui.org/#51)), or sell in limited quantities ([#36](http://www.goodui.org/#36)).

Another thing to consider would be the the perception your website or storefront has on the prices your customers expect. The concept of *horror vacui* is why low end retailers (like a dollar store) tend to have very cluttered websites or stores with no space left empty while higher end retailers (like Apple) tend to have more minimal pages or storefronts with ample empty space. 

You'll have to decide if you want to create a user experience that leads customers to expect low prices so they know what they are getting, or one that leads to expectations of higher prices (and higher quality) so they are surprised by the prices (and hopefully not disappointed by the quality).
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> Perhaps strike through list prices and show discounted prices in red
> 
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I think most people realize there's a level of bullshit involved with that. Test, obviously, but in general, I'd avoid that altogether. If you want to show that your prices are especially low, consider showing competitors prices along side. 

In general, the best way to show affordability is just as you suggest: focus on prices and have the business make sure they are good, affordable prices to begin with. 

Beyond that, there's likely a level of marketing and branding that needs to accompany this.