Definitely agree with the "don't ask", "don't get" mentality

Remember that most retailers have enough of a profit margin built in so that they have some room for movement on price.
With electronic equipment there might not be massive discounts to be had on the main items, but buy your consumables at the same time and you could be in for some huge reductions. Many of these have from 100% to 200% markup on them!
Give it a go and let us know what you get.
A while back we were working long hours at work and ordered food in a couple of times. To keep our sanity we had a bit of a challenge going within the team. The person who ordered the food had to try to get as many freebies as possible. . . The winner? An order of 6 large pizzas (paid for); 8 large bottles of soft drink (free); 3 garlic breads (free) and 4 side orders (free)

Totally beside the point, but I thought I'd share.
Regarding the benefit to retailers of cash over card payments, as has already been said there's little incentive to retailers these days to take cash.
I'm an accountant by trade and I used to work for a national retailer.
Although there is a charge related to credit card / debit card sales a lot of the time this is outweighed by the cost of taking cash :
Cost of banking services.
Cost of Security collections - not many retailers physically take the cash to the bank themselves any more.
Extra staff time in cashing up and preparing banking at the end of the day.
Additional insurance costs in line with the amount of cash expected to be on the premises.
Higher risk of fraud.