You can search the archives but I'll give you my .02
In terms of the readers they are free if you are using a program like "square" (google it very simple to use and worked for me for my first 2 years.)
For your typical residential and even most commercial clients you can get by with square or paypal or similar who all offer readers.
They all have rates for each transaction which is based on a percentage of the transaction.
For square it used to be 2.75% with the card in hand swiping it with the client there. It is a bit higher if you get digits over the phone from clients who call you with their number but still fair enough.
You can put a clause in your contract if you don't want to eat that 2.75% or whatever you are paying to the service, we did the first two years that stated "we accept cash, check and if credit card is desired a 2.75% transaction fee applies).
Nobody balked, it used to be illegal but stopped being so at least a year or more back...
Anyway, I was fine with square until one of my government clients for bird work had a purchasing manager who noted that square and paypal are third party companies.
In other words they aren't banks.
So I signed up last year with Bank of America Merchant Account Services. Again fees apply and there is a monthly fee with them too.
Some guys on here have a variety of companies and have found great rates and deals.
You can shop around, they all work, simple is best in my book.
I still use square when I want to, but all of them use Apps that work on your phone, you login with username, password and then enter what you are billing for, plug in the swiper device (tiny little things) and swipe and have your client sign on your screen of your phone or pad with a stylus.
Done deal and your cash is in their within 24 hours to 72 hours depending on which service and so forth.
Square was pretty fast, BOA takes a few days but no big deal.
Hope that helps, its all I know about it, to me they are all good, just fish for the best deal for yourself and your company!
Best,
Justin