1) What will it cost? Now this is a tricky question and it depends on how you measure and see currency. As an example, if I buy an ATV on Craigslist and pay $3,500 for it, that's a clear transaction. The cost for the ATV was $3,500. I gave $3,500 and in return I got an ATV. My money is gone and in it's place I have an ATV.
So what does it cost to give 100% of your life to God? Well, I have 24 hours a day now and if I give it all to God, I still have 24 hours. What may be different is my priorities and agenda with those 24 hours, but I still have 24 hours to spend and invest in relationships, ministry, work and life. For me (and it's a daily process, take up your cross daily) that's pretty much what my life is. On the one hand, I'd say I've already given my life 100% to God, but on the other hand, I need to remember to do it daily, every day. So many distractions, temptations, etc. which is why it's a daily process.
So what does it cost to give your life 100% to God? I'd say it's like buying the ATV for $3,500 except... a) You get the $3,500 back with the ATV and God says, use it wisely my servant. Give generously. b) You get a bigger better ATV (like the one you bought, but newer, new tires, EFI, and all the extras). Yes, that's what it's like when you give 100% to God. You get it all back plus extra and a spirit of freedom, peace, joy, peace, patience, etc. Not a bad deal.
I think we've answered the other 4 questions already: We get a new better life. Yes, it's worth it. Yes, I want to do it. It looks like fun, freedom, peace, purpose, joy, etc.
Here's a few verses on the topic:
Mark 10:28-31 ROI for investing in God.
Rom 12:1-2 Giving it all to God
Mark 4:19 = life of distractions. Mark 4:20 = multiplying the investment
1 Cor 3:10-15 Consider carefully how you build/spend your time
Heb 12:1-3 Run the race, don't be entangled in sin
2 Tim 2:4-6 Don't be entangled in the world's ways, but race and compete...
Col 3:17 & 23 Whatever you do, do it for the Lord (whole chapter is great)
Luke 9:23 Take up your cross daily
Phil 2:3-4 Consider others needs above yourself