I was there for that fire, actually (and several others in your area, including the Milleville and Patch fires.
The DC10 pricing schedule is a little different than what you posted, but it's also complex, and the hourly rate varies with the retardant load. In a nutshell, tankers are contracted at a daily availability rate, which means the value they're paid to be available on a day to day basis to fly. It may sound high, but that's the cost of maintaining that aircraft, crew, and everything that goes with it in a configuration to fight fire, for the year, amortized over the number of expected days of available use in that year. It sounds high, but it costs a lot to make an aircraft available, and while it may only be used for a few months, it's worked on and maintained all year; it makes its money during the fire season.
The hourly rate is in most cases a fixed value, but the DC10's rate varies with the retardant load, and is actually contracted at a very low gallons value. As more weight is carried, the cost goes up on a sliding scale. It was bid that way for competitive reasons, and worked well.
I dropped right behind the DC10 several times recently on some large fires. One one particular drop being done for structure protection, I came down the canyon to pick up a spot fire that remained after the DC10 went through. It was a very steep run to the target, and when I got there, at low level, I was surprised to see the amount of standing retardant pooled on the ground on the line. It laid out a heavy line, which given the wind and threat to the town, was a very good thing. It also laid a long line quickly, and while it had to come a long way to the fire, it made a very effective drop that was needed at that time, in that place. It's not the idea tool for all drops due to size, cost, and numerous other factors, but as is often said of various tankers, it's one tool in the toolbox.
The primary job of the tanker is to make things safer for the firefighter on the ground. We don't put out fires. We use tactics to modify fire behavior at the direction of ground firefighters to accomplish their aims on controlling wildfire.
Contracts exist generally either as CWN (call when needed) or exclusive use. With CWN, aircraft exist as free agents of sorts, and are moved and called where required. They can be picked up for a fire any time, and released at any time. Their pricing, availability and all terms of their use is governed by a CWN contract between the vendor and the government. The aircraft and crew is utilized very much as government property, going where it's told, when, and how.
The exclusive use contracts have time values attached; a 90 day contract, for example, is let for a particular base, and bid by the vendors. If the aircraft is awarded that base and contract, it's still a national resource, but has a guaranteed availability value for the term of that contract, plus pre and post-use, which is almost always used.
There was a lot of talk here about Neptune and the recent contracts, but most who posted had no understanding of the process. The "next gen" contracts were (are) political, and were awarded to aircraft that either don't exist, aren't legal, or aren't available. Neptune's P2V's are reaching the end of their life, some of which don't have enough hours left in them to complete the season. Neptune wasn't expecting extended contracts into the next decade for their P2V aircraft, because they'll be replacing them all within the next five years or so with BAE-146's. This season two of their aircraft, T140 and T141, have been flying heavily. Minden is also doing their same with their BAE146, using a different tank configuration. Neptune intends to replace all the P2's, and I believe should have ten of the turbojet aircraft on line in the next five years or so.
Ultimately, the aircraft use is about effectiveness. It's about safety, and it's about being able to use the right tool at the right time to bring about the objectives of the incident commander on the ground. When costs are considered, one looks at the cost per gallon delivered. In some cases, the DC10 provides the least expensive value; a lot of gallons delivered in a short time, vs. multiple trips by other aircraft, but that's only part of the picture. Being able to build long line in one shot, rather than multiple trips back to the fire, is a very critical part of the picture, because the fire is constantly growing and changing, and if the line can't be built quickly enough or the wind shifts during the building process, the fire can change quite dynamically.
Conversely, sometimes the most cost effective method is a SEAT (single engine air tanker), operating close to the fire, making tight drops in confined areas, multiple short turns. The DC10 might be coming from two states away, while the SEAT might be ten miles away. The cost per gallon delivered depends on a number of factors, and the value to the fire is a lot more complex than daily numbers. It's also a lot different to those being evacuated and about to lose their homes, and very different again to those on the line who might lose their lives while fighting that fire, or those on the ground who aren't fighting the fire, but who might lose their lives anyway. I've been on several fires in which that has happened, including recently, and the dollar cost is nothing when framed in that light.