Seems pretty high at $5,000....Back in 2010 when I bought my new Tacoma the dealer also offered me an extended warranty..it was around $3500 as I remember...and I did buy it...BUT canceled the next day after I thought it over and did some research...So,what I learned....you do NOT have to buy the warranty from the dealer you buy the truck from....in fact there were 4-5 dealers I contacted in the Mid-West (I'm in Pacific Northwest)that were hot on my ass to sell me a policy for $700...YEP..same exact policy....Its like any "part" you would buy for your truck...why is it $99 one place $149 another and $200 at a 3rd...same part....sounds like your dealer has a pretty high mark-up...although I dont know what a policy today cost,I'd bet you could get him down at least 1/2...he wants to sell you that truck...you can dicker on a warranty just like the price of the truck.I dont remember the dealers names,but if you Google "Extended Auto Warranties" you should have plenty to research...
As far as is it a good idea....well,I finally told ALL the dealer,I dont want it....drove the truck for 60K...sold it for a great price,and never did anything more than change the oil...BUT...with a 98K vehicle....its a crap shoot...Ive only bought an extended warranty once years ago when VW introduced the Turbo Diesel...it was new tech at the time,car was 1 year old with 8K on it....so I figured I better buy it...3 months later,engine blew....and I was covered.....IMHO...at $5,000 I'd pass....but if you can get him down to $2K range,....I'd go for it....just make sure to read the fine print....they are like ANY damn insurance co...they take your $$,and they cry or say its your fault when they have to pay out....
Good luck..!!