If you have a used Honda Trail 70 that is not in good running order, I'm thinking the most you could expect to get for it is $200.00, and that's being generous. Personally, I LOVE the Honda Trail 70 because I grew up riding one, but you have two problems here: (1) It's not a high-demand bike, and (2) It needs work. Heck, I had a colleague who simply gave me his 1980 Honda CB650 Custom street cruiser because it didn't run and he was looking at $500.00 to $800.00 to get it back in running order...
How much will it cost to re-wire it? That depends. If you have a Honda dealership do it for you, it's not going to be cheap -- be prepared to pay $200.00 or more for that job. If it's just a case of old wires that need to be replaced, you could save a lot of money by buying a complete wiring harness from Honda and having someone who has a decent knowledge of electronics wire it up for you.