What's the bus cost? How long does it take? Any tips?
About an hour and a half and it costs 1,200 Colones ($2.50 ish). You can use a Tica bus but you have to book it and stand on the highway etc. and its not worth it.
Walk across the border and take a bus to La Virgen for less than a dollar (Its 15 Cords but you may get a gringo price).
From La Virgen, bus 10 - 20 Cords or cab 30 Cords to SJdS.
Cab from the border to SJdS expect up to $20 per person but $10 is good.
Border: Have $12 exactly for entry to Nic and one dollar to enter the gate after that.
I'll give my best shot.
with a car?
What are the specifics?
See http://www.nicaliving.com/entering-leaving-nicaragua for this and so much more.
Get your facts first, then you can distort them as you please
— 'Mark Twain', Samuel Langhorne Clemens