Did the drive in two days once, when we were in a hurry. If you are by yourself probably best to plan on three or four days.
The toll roads will be happy to take whatever money you have. Many now will just send you a bill in the mail, if you don't have the EZPass or whatever is required. You can avoid most or all tolls by taking I70 and I64. That route is probably a little longer than I80.