You have explained to them that their carcass will weigh 62% of their live weight, and they will get about 2/3 of that weight to put in their freezer??
So, if he gains 100#/mo, he will weigh 1300# X $3.50 = $4550 x 62% dressing weight = 806# less 1/3 = 532# for the freezer.
So, that's $4550 for 532# of meat = $8.55/lb
Out of that 532#, there will be ? about ? 120# of meat that can be made into good steaks. The other 412# also costs $8.55/lb.
https://www.google.com/search?q=beef+cutout+sheet&rlz=1C1JPGB_enUS786US786&tbm=isch&source=iu&ictx=1&fir=bXtj-6UoTNLmeM%252ChYUN6Z2vY613bM%252C_&vet=1&usg=AI4_-kR4-8cSKX9eb-FGpAXKPT-FJCVRMw&sa=X&ved=2ahUKEwjcy8u8-6fqAhXwgnIEHdckAF4Q9QEwDnoECAoQLA&biw=1536&bih=755#imgrc=7JLmPA9JbBZo8M&imgdii=_3PPEyehUBlG2M
If they understand that and are happy at that price, go for it.
Price of carcasses currently by USDA for choice is $1.72 - So, your steer is worth about $1400 on the current market. Like I said, if they know what they are getting and are willing to pay, great for you. Of course, you are in California.