A lot of these recommendations won't work well for you.
An 18" deep box is great for a guy in his garage, but won't last long doing mechanics for a living.
Not that the hf 44 doesn't seem to be a pretty good box, I have the matching drawer bank hanging on my cart and its pretty sturdy and has given me no problems.
But an 18" deep box will fill up almost instantly. Especially if you buy stuff in sets and keep the tools in their molded cases, some of which you almost have to.
A 50-56" x 22" is the smallest box I would consider if I were you, and really a 24 or 25" deep box would be much better.
Having had many different tool boxes I can say the extra depth gives you more practical storage than the numbers would indicate.
I'm sure others who have several different depth boxes or have gone to deeper boxes will agree.
Mainly because if you have to turn something longways to make it fit in a drawer it pretty much takes up the whole drawer, maybe leaving a little on the end. If you can put it in a drawer the other way it only takes up a 1/4 of the drawer or so, maybe a 1/3 - depends on the set in question.
So instead of getting 3 or 4 sets in a drawer, you only get one and a bit of odd space, and sometimes a long skinny space at the back.
A 30" deep box is even better storage wise, but can be an issue making room for, and are more difficult to move, both in the shop and from job to job.
Given you are fairly new to the field you probably move jobs a lot, especially at first.
I've moved my kr660b by myself with just my pickup several times. Put the tools in 5 gallon buckets, pull the drawers, lay a piece of cardboard on the tail gate, tip the box on its side with the fixed wheels up, back the truck up close to it and tip it ahead until it hits the cardboard and then pick it up and in. Its a bit heavy at the last point, but doable, especially if you can get a hand right when you pick up the end - then its easy.
You can then then put the drawers back in, strap it down, and put the buckets in around it. (a 5 gallon bucket holds a lot of tools.) If you moving a short distance, and/or under pleasant circumstances you can do the drawers in a second trip and its quite a bit easier.
With a 30" deep box this isn't really practical. They are a lot heavier generally speaking for one thing, also I doubt if you could put the drawers back in, or at least the lower ones once its in the back of a truck, so realistically you would need a trailer to move it.
And if you have to find a place to put the box in between jobs, a 54x30" box is a monster, hard to get through doorways, etc....
On the other hand you can often pick them up proportionally cheaper for that very reason.
I recently bought a krl1001 in decent shape for $1000, he delivered it to my work for $75 and I bought carpet runner for drawer liner at lowes for about $80. Then another $20 or so in cleaner/lube and a weekend of casual cleaning/lubing/cutting liner and I have a really nice box for under $1200, and its old enough I'm fairly certain its paid for. (1997)
The comparable new box from snap on lists for $9050 - plus tax, and its pretty much the same box except the new one has 2 full length top drawers instead of 1, but it also has fewer deep drawers which is also less handy these days.
You definitely want more deep drawers also - once again, cases. Tap and die sets, puller sets, meter cases, Scanner, etc... all come in cases, or are themselves too big to put in a shallow drawer. You want some shallow drawers of course, but not mostly shallow, and definitely not all.
The 72 x 30" boxes, or even the 72x24" boxes are generally sold for even less proportionally, because they are even more of a hassle - but they are more of a hassle.
I see a Krl7023 on my nearby craigslist for $1500 and looks to be in ok shape for example:
https://tampa.craigslist.org/pnl/tls/6015109758.html
I see the classic 78's for $1500ish fairly often, but I have some doubts about whether or not they are paid for.
Still higher than you want to spend I understand, but even better ones do pop up now and again.
I was in the middle of moving (house, not job) about 3 months ago and couldn't go get it, but there was a kr1000 for $350, but it only lasted about 4 days before it was sold.
Nice guy, offered to hold it for me, but I didn't want to do that in case things didn't work out, said it was in good shape and I believe him, pics looked good and he was an older guy with a farm who just didn't need it anymore.
But for that price if the drawers worked okish and it wasn't battered to death it was still a good deal.
So deals are out there, but be ready to jump when you see one, but give whatever you see a good look over.
