To figure the cost of something you have to take the price you paid for it, subtract the price you eventually sell it for, then divide by the number of times you actually use it.
A good quality bike will last a long, long time if it is properly cared for. While a major crash can end the life of any bike prematurely under normal use a life span of 20 years or more is common.
First off, a CRF 80 is way. way too small for you (unless you are really, really small). You should be looking at a full size bike. An adult riding a CRF 80 is just asking for trouble, both in terms of damage to the bike and the likelyhood of it throwing you over the handlebars.
You could buy a 10 year old MX bike (Yamaha YZ-250, as an example) that is in great shape and fully race capable for under $2000. Or, if you are not that aggresive, buy a 5 year "off road" bike (such as a Yamaha TTR-250) for even less. If you decided that you didn't like it you could turn around and sell it for the same thing you bought for. Or you could keep it a few years and sell it for a little bit less. That $2000 YZ would probably fetch $1500 in a few years if you kept it up.
That "replica" is probably worth next to nothing the instant it becomes yours. While it might replicate the look I seriously doubt that it would replicate the quality and the durability. When something on it does break you may find that replacement parts are hard to come by. I ride a 1986 Yamaha YZ-125 and for most of the common repair parts I can still order OEM parts from Yamaha! Before you buy that replica find out what it takes to buy a top end engine gasket set.
My advice is to stay away for the replicas and to buy a bike that is suited to you.
Rod