I figure if I'm going all out, I should add another room up top. This way it has horizontal and vertical tunnels. I *believe* (not sure) that the number of ballast pods shown will be sufficient to restrain the added volume of air, I'll have to run the numbers again to be sure. If not I can always add another ballast pod. Here's the cost list, allowing for a 3 or 4 enclosure final build, and either 4 or 5 ballast pods depending how many are ultimately needed. It's possible to get slightly lower prices for some items but not from trustworthy sites. Total dry weight for the 4 module version is around 53lbs.
(All prices include shipping)
Otterbox 9000 x 4-5 = $61-$74
Lexan Drybox X-Large x 1 = $49
Otterbox 3500 x 2-3 = $41-$57
Acrylic tubes x 1 (cut in 3 inch lengths) = $17
5lb Lead block weights x 8-10 = $224-$280
Nuts and bolts: $3
Custom metal plate: $???
So, metal plate aside the final pricerange is $395-$480. That is to say $395 for the original Mark V design with only two additional rooms, or $480 for the revised version seen above with 3 additional rooms. Any parts not accounted for in the price list are items I already have on hand. The big question mark here is how much a custom milled steel plate with a waterproof coating is going to cost.
Bonus madness you never asked for:
To put things in perspective, the conceptual monstrosity below (aka Hampture Ultimate) would cost around $2,000 assuming the component prices listed above. I sometimes do "what if" designs like these which assume no limits to funding and access to a private pond or swimming pool. At a dry weight of 350lbs I'd need either 3 strong friends (each capable of lifting 87lbs for moderate durations) with scuba gear to help deploy it, or a small crane. Like it says, this would be a permanent city, not intended to be surfaced.
And so long as we're going nuts, let's give 110%. Hamlantis is a permanent underwater world for hamsterkind inside of an 8 foot diameter transparent acrylic dome mounted to a round metal 'dish' with a hole in the center where a human diver can surface to manually transport food, water and additional hamsternauts to this awe insiring waste of money. I cannot even begin to calculate how much this would cost although I do know that a 5.75 foot diameter dome runs $617. I couldn't find the place I inquired with before that sold 8 foot diameter domes but sufficed to say the prices were banaynay. Worse yet, the total amount of lead ballast weights needed to keep this retard's fantasy from floating is 1.1 tons. This would require a boat trailer, removable floats and several friends with scuba gear to deploy in a lake.
This would be large enough to comfortably accommodate one cat, and (uncomfortably) one human being provided he lay on his side. With a dually redundant set of electric automotive air compressors, this shining monument to obscene first world decadence could be deployed a full 25 feet deep, with the "moon pool" (open floor hatch) at 21 feet, the limit before which saturation doesn't occur, and decompression will never become necessary regardless of how long you stay there. And staying there would be a foregone conclusion, due in part to the immense difficulty of ever removing it from the lakebed, and also because there would never be any need to. While not strictly self sufficient ( I experimented with plants and ran into mold problems) it could be supplied with dry food and water sufficient to last a year. With so much space and their instinct to shit in just one specific spot, waste buildup wouldn't become a concern for months. And cleaning up that spot, or delivering more food/water, or adding/removing hamsters (I estimate this thing could sustain at least 100) would be as simple as swimming down there with scuba goggles and a micro scuba bottle (aka Spare Air 3.0cf) and a watertight case holding whatever I'm transferring to/from the dome. And yes, that's a heat lamp suspended at the end of that boom. It's their miniature artificial sun.
This could be done. It is absolutely possible. SHOULD it be done? Under no plausible circumstance. But if anyone out there is rich and has a burning need to witness Hamlantis or Hampture Ultimate brought to appalling, ill-advised fruition, I'll do it.