It totally depends on what kind of an experience you're looking to have. If you're not looking for a 5 star experience, then yes, you can absolutely more than get by on $140/day.
My sense, based on the trip that my wife and I are just finishing up, is that Peru can be as cheap or as expensive as you make it.
For example, if by "souveniers" you mean some scarves or trinkets or things like that, then yes, you can get those for like $5. But if you're looking to get some Baby Alpaca cardigans from the boutiques, then they'll run upwards of $150-200 each. Similarly, you can get a relatively good meal for like 20 soles ($8) from a local place. But if you want fine dining, 4 course meals at an upscale restaurant, you'll still spend around $40 (or more if you drink alot).
The full Tourist Ticket (good for 10 days I think) was 170 soles.
Have fun! We mostly enjoyed our time in Peru.