Get the best meat that you can afford.  You'll still get a lot of the benefits of paleo, even if you are eating commercial meat rather than grass finished meat - especially if you are eating pasture eggs, which will help with the omega 3s.

The worst part of commodity beef is...fat! (On the other hand, once the meat is organic and grass-fed, fat is the best friend).
Mark Sisson said that folks who just can't afford it, should go for leaner parts (e.g. round steak) and supplement their good fats from fish oil. There are very good and inexpensive versions on iherb. They are third party certified but are much cheaper than nordic naturals etc...

I admire your commitment! Keep it up.

I'm also in the same boat. For the most part I buy "ordinary" quality meat but I'm careful as to the consumption of said meat's fat. Recently I discovered that a local supermarket is starting to stock grass fed beef for a relatively cheap price. I tried it out and the fat was SUPERB. It literally blew my mind.

So, grass fed is worth it but otherwise get some good butter like Kerrygold and supplement your fat intake with fish oils, avocado and coconut.