By the hour also. Are the stripes on concrete or asphalt ?
If the property owner is having the parking areas re stripped, I have found that the stripping company will usually outbid the removal and make up for it on the stripping.
Let me know how the bid works out for you.
I have had some lines that come off like they were scared of water. I have had other that Jasco stripper and a turbo wouldn't completely remove. The ones that would not remove the concrete beneath the stripe was etched, which allowed the permanent adherence, and made the stripe impossible to remove with stripper and high pressure/heat.
I would suggest doing a sample stripe. This will give you an indication of how much time and what materials you will need to successfully remove each stripe.
Stripe Hog and United Rentals has high pressure water blasting equipment to remove stripes, but are both expensive is not equipment you can just rent.
http://www.ur.com/files/corp/catalog/134-139_highwaytech.pdf
http://www.waterblastingtechnologies.com/WhyTheStripeHog/tabid/227/Default.aspx
I have had great luck with taginator. I usually get $1 a foot.
I have watched some movies of the Stripe Hog on YouTube in the past and I was impressed. Unfortunately, this machine costs lots of money an my biz is not dedicated to only stripe removal. It is more about small jobs that come only once in a while.
This is another one that came today: 145x4" single lined parking spaces painted with yellow latex based paint over a concrete. I agree spot test is the best way to figure a price, but I am not able to do a test prior signing the contract on this one .
If it's latex paint, it should come off real easy. If you want to try Taginator, you can get it online at ETS and get free shipping with a couple of their value packs;
http://www.shopetsonline.com/product-p/cpcp-2048-vd02.htm
Not sure what your environmental concerns are on this jobsite, but if it isn't a concern Jasco makes a great paint stripper. Roll it on with a 4" roller, let it dwell then hit it with pressure and hot water.
But the latex stripes should remove with just pressure.
Go do a test spot first.
I would use something thicker.TRY smally co.they sell a fast acting stripper.I have used it many times .IF they are really on the tag is to thin.I have removed entire parking garages with this.it will take multi-layers.large garages we use a water jet way cool to use. GOOD LUCK..p.s i would be around 1.00 also rememger you have a mess to clean up.