First off I own seats in 129 and they are 99 a piece for cost and thats not including taxes, parking, etc. thats what the ticket reads. Stubhub will charge more than cost for tickets.
If you look at the stadium in the picture, there is a break in the 100s and 200s. In most cases you still go through the same tunnel, but the 100s you walk down into and the 200s you turn around and walk up stairs. The club level is above this inbetween the lower level and the upper level (400s) The club level has its own entrance and costs alot more than anywhere else in the stadium other than the luxury boxes.
Bargains IMO hard to find at the stadium especially before the season starts when optimism is high. If you dont mind sitting behind a concrete post or limited view I would suggest Obstructed View Seats although I would never sit in them. They are cheap but you can only see half the field in many cases, but they do provide monitors and they are under cover if the weather is bad.
Upper level is definitely the cheapest because its way up there. If you could find lowers in the 100s or 200s for $100 a piece that would be optimal.
Hope the info helps.