1989 F-150 are engine bearings expensive or hard to replace?

Ther are no such thing as "engine bearings". They are lying to you. And yes if it is ANY bearings in the engine, ITS A BIG JOB. Dont buy it without a professional diagnoses.

If the truck is in great shape other than the engine, and can get it at a good price, go for it. Just purchase a reman (not rebuilt) engine and have it installed. If you're contemplating pulling the engine from the vehicle you just as well rebuild it while it's out. If you've never rebuild an engine before, do try it. You'll waste your money.

i have rebuilt a few beaters, my first concern is why are the bearing shot, most 300 sixes with care should of put the truck into grave yard i have seen them running good at 250,000 miles on them. if it was abused hi RPM, and neglected oil, or some other problem like slinging oil off the side of a rod bearing that is causing low oil pressure. it could be a lot more than bearings. I have done poor man overhauls with bearings, cylinder honing and new rings and cheap valve job for under $300 on wore out but ok motors and got another good running 100,00 miles out of them. I have a $50 68 390 Police Intercepter that happened to be in good shape, But a low oil pressure motor will have everything shot from the bottom end all the way up, stuff like rocker shafts, cams, cranks and pistons get expensive quick, if you do go thru it is a good learning experience.

Good idea cheap. Nothing like getting one's hands dirty to reduce the learning curb.

some of the best lessons i have remebered well is what not to do again. I was fortunate to have been mentored by an old goat that could fix the crack of dawn and broken hearts, with ready available parts out in the backyard junk pile, there are many things that you can get by with, but things like cranks and rods can be unforgiving. hell just pull the pan off pull a bearing out to make sure its a standard Bearing buy a set and throw them in. It might go a while if your lucky, by lottery tickets to if it works. Most used car lots would do the same thing,

I assume they mean crankshaft bearings?

No, your knock is probably comming from the Rod bearing- It is possible to put them in without pulling the engine or the the head, the oil pan must come off and you have to rotate the crank to get at the rods. it can be done BUT if the motor is already been hammering on stuff your rod connecting rod journals may have been hammered egg shaped, they are checked by unbolting them and taking it off the crank -putting the cap back on and retorquing then using a inside micrometer to check for roundness, you should use a micrometer to see if the crank shaft is close to tolerance measureing it in different sides to see if it is close to round. All of this is painful to do while still in the truck, when you put new bearings in to take up the wore out stuff and tighten up the connecting rods (which are now egg shaped) the motor could likely not rotate anymore because it will be too tight to allow it to turn. The Crank shaft jornal bearings that hold the crank to the block would require the motor to be pulled. So you need to have specs on the crank and stuff, a little idea of what you might be able to get away with.

easy answer, yes they are cheap, and yes they are quite hard to change