Property tax protest companies

[Viral Mehta]

Hello,

I am a remote investor and I own 3 investment single family homes in North Dallas (Frisco, Little Elm and Van Alstyne) that i have purchased withing the last 12 months. Compared to the prior year's assessment, the tax assessed values have increased between 30 - 50%.
1) Can you please let me know the names of property tax protest companies that you have used and like in North Dallas.
2) They seem to charge 40% of tax savings - does this sound reasonable?

Also, my home in Van Alstyne has the tax assessed value below my purchase price. However the tax assessed value has increased from $200K in the prior year to $302K this year. Though I paid $305K, is there a chance I can successfully protest the 50%+ increase? 
3) Van Alstyne does not allow remote protesting for non-homestead investors and I cant find tax protest companies that service Grayson county - does this mean I am out of luck? 

Thank you for your help.