I stripped this ATV down to nothing and rebuilt it from the ground up.
I've only put between 20 & 30 riding hours on it since then (about 3 years). I've been turning wrenches for 18 years and did most of the work myself. Here's what has been done, and the cost to do it.

Honda TRX250x
A decent, complete machine runs $600-$800 to start with. I originally gave $750 for this one about 10 years ago.

MOTOR
-Totally torn down, cleaned, and parts inspected. $10 worth of parts cleaner
-New oem Honda crank bearings $70
-New Vesrah HD rod kit $105
-Custom 3mm offset stroker crank pin $45
-Crank assembly and truing $75
-2mm overbore on cylinder $50
-Wiseco 12:1 forged piston $125
-Oem Honda timing chain $39
-Performance head port and polish $300
-Kibblewhite "Diamond" valves $120
-new Vesrah valve spring kit $65
-New Barnett clutch kit $89
-All new gaskets and oil seals $70
-Timing advanced 3 degrees @ crank sprocket
-Custom built dual exhaust with straight through repackable cans, started out as a Katana 600 4 into 2 $100 for the exhaust from cycle salvage, about 10 hours to build and fit. Labor at a welding shop would run $400 at LEAST.
-Custom built sprocket cover/case saver $20 buddy deal
-Polished aluminum motor side cases I don't remember how many hours!!
-Washable cone style free flowing air filter $23
-Rebuilt and custom jetted carb $24 kit drilled original jets & tuned with plug readings. Set up a little rich (better safe than sorry)

CHASSIS
-Frame stripped down and painted $40 worth of stripper and paint
-Stock swimgarm lengthened 3" $10 buddy deal
-New axle bearings and seals $29
- New standard duty sprockets and chain (12 tooth front) $50
-Honda XR500 comp/rebound adjustable rear dirtbike shock (set up for a 220# rider) $75 used cycle salvage
-DG steel nerf bars $100
-stadium style aluminum front bumper $60 used
-Custom built Aluminum rear grab bar $50 buddy deal
-Nice stock front shocks that work great, cleaned and repainted
-New steering stem bearing and seal $12
-New Moose carbon steel handlebars $18
-Custom headlight mount with 55w halogen driving light $24
-Rear master brake cylinder with screw on lid $10 used cycle salvage
-oem plastics prepped and painted with PPG silver metallic basecoat/clearcoat $80 worth of paint and supplies
-seat recovered with marine grade silver vinyl $20 for vinyl
-all brake calipers taken apart, cleaned, and re-assembled
-front master cylinder rebuilt $25
-parking brake removed and blockoff plate installed $10 blockoff buddy deal
-all-in-one clutch/e-brake/reverse lockout removed. Has regular clutch lever and small seperate reverse lockout lever. $10 for levers used
-4 decent used tires, mounted $75

Check up on those prices for yourself, I have a lot of money and labor invested in this thing. We don't ride ATV's anymore & I have already sold my wife's and my son's.