I bet there are guys around who could figure out how to make a rock solid vehicle for far less than that that would be bullet proof and ridiculously durable and smooth driving. This is why we need to pool our brain power and put together all the best elements and figure out how to solve these issues properly IMO.
No offense, but this message forum has about a 15-year headstart on your idea....
You may have just found this site, but we've been talking about stuff like this forever.
The problem IMHO, is that the vast majority of guys are seduced into taking their builds right past "durable and smooth riding" and into the realm of the mythical "ultimate wheeler".... (whatever THAT means)
During a build, there are many times when you need to choose to take the truck either more radical (and less practical) or more reliable (and less offroad capable). Most guys here will choose the former category... A simple example is tires. A great "practical" choice would be a 35" radial tire. It provides good ground clearance for offroading and will still drive nice and quiet down the road and will balance properly and not shake you to death..... Problem is, nobody here buys 35" radial tires!!
I blame the internet... and this dysfunctional group of CK5 members.

. There are SO many guys here doing builds and doing fun-looking stuff that it's easy to get "upgrade fever"... If 35s would be good, then 37s must be even better.....and 42s are even better than that! The same thing applies for softer leafsprings..... 52s must not be as good as 56s....and 63s must be the best of all?!
The problem (if you want to call it that) is that a well-rounded, capable and reliable truck isn't very "sexy" or "radical looking" so most guys don't make that their goal when they start building.
You want an "off the top of my head" build sheet for a comfortable, reliable K5 for less than $30K? Here it is...
'69 - '91 K5 - Get the cleanest and most rust-free one you can find.
LS motor swap - Very common now, inexpensive and practical
Automatic transmission / NP241-type t-case - deep offroad gearing for cheap.
35" - 37" radial tires - Thats the max if you want a true dual-purpose truck
Custom leafsprings - not too long/soft, maybe 350 - 450lb/in rate to get necessary lift and softer ride
Good shocks - high quality shocks (and I don't mean Rancho!) are a must.
14 bolt rear axle with ARB - Selectable lockers give the best street manners
D44 front with selectable locker - You don't need a D60 in this tire size
4.56s or 4.88s - Good ratios for the larger tires without losing all highway capability
Rocksliders - Protect the body
Skidplates - Protect the underbelly
Rollcage - Protect the occupants
High-clearance bumpers - allows for the winch mount if you want one.
Quiet exhaust - don't throw a set of 40-series Flowmasters on a truck that needs to cruise on the highway.
Dynamat - Lots. Kill as much interior noise as possible
Rhinoliner / Line-X - same idea.
A/C - Working air conditioning (and heat) do nothing to improve performance but make driving a lot more pleasant
Those are the basics. Like I said, it's not a "secret formula"...most guys don't gravitate to this type of mild and practical setup.
-G