As long as you have the strength and flexibility necessary to ratchet the bolts holding the head onto the block, there’s no reason why this couldn’t be a diy’er job. An engine is constructed like a layer cake, with frosting between the layers, and what you want to do conceptuallly is just remove the top layer from the bottom layer, put in some new frosting, and put the top layer back on.
$$- and time-wise, as a novice diy’er, expect this job will take quite a bit of your time. Figure a 5 days full time effort, 40 hours or your own personal effort or so. An experienced shop tech could probably do the job in 1/4 that amount of time. The reason is that they already have all the tools on hand and have done the same job many times before. But that time comparison diy’er vs pro is no reason for you not to do it yourself. It will just take you a little longer is all. If you have the time to do the job, won’t be a position where you’ll have to rush things, besides renewing your head gasket, it will be a good learning experience. You’ll be able to build on what you learn and do a lot more diy’er fixing, so figure the future cost savings into the equation too.
As far as what’s involved, for an engine like what many Rav 4’s use, the 4-banger 1az-fe, there’s probably about 20 individual steps to remove the cylinder head, and the same number to put it back on again. Plus however many steps are involved in replacing the gasket itself. Most shops wouldn’t just replace the gasket, they’d send the head out to a machine shop to make sure it is perfectly flat, and the macine shop would also do a visual inspection of the valve situation, to see if it might be a good idea to do a full valve job on the head, or replace the valve guides and/or their seals. I’d recommend this machine shop step for your engine too, especially if your engine has ever overheated. Not an uncommon thing for engines with head gasket problems.
If you decide to go for it, don’t try to re-invent the wheel. Get Toyota’s written procedure, then all you have to do is follow it step by step. If you get to te point where you need a special tool, stop what you are doing and go get the tool. Don’t try to do it using mickey mouse methods, that’s how diy’er get themselves into $$-consuming trouble. Best of luck there OP, be sure to let us know the result!