Opportunity to Buy a 2004 757

Greetings all...I am new to the forum and am looking for some advice. I have an opportunity to purchase a 2004 JD 757 Ztrak mower that has 314 hours on it. The person who is selling it just purchased a larger Kubota ZTR and is selling this one. I will be using it to mow ~3 acres. He is offering it to me for $2500, which to me sounds like a very good deal. I have looked it over and driven it and it appears to be in excellent shape. (This person actually works for me and has for the last 3 years...I trust him completely). The hydraulic oil and filter have not been changed since new, as the manual says to change it every 500 hours...but it also says to do it yearly? Regardless, if I buy it I will be changing it, and the manual also says to check the valve clearance and lap valve seat surface, which has not been done yet. I have adjusted valves on a car engine, but never a mower, and have never heard of having to lap the seat surface as regular maintenance...any idea what I should expect to pay to have the dealer do this? Sorry for all the questions...just new to the ZTR and JD world...any advice or suggestions would be appreciated.

Thanks!