Or you could find someone who's getting out of the hobby. Or at least unloading 90% of their modelling projects. Like myself. I have a little boy, and a house to fix up, so between them I don't have the time to finish up my ork army.
I still get to use my modelling and painting skills, only now it's a house. Plus side, power tools are fun. My wifes face when I mooted buying a nail gun. Anyway...
It's fairly large, I have probably a green tides worth of boys. I was planning big mobs of snakebites and grots using
WHFB models on
40k bases, plus a ton more
WHFB boys.
I've also got 40-50 partway built scratch built lootas. About a dozen dethkoptas cut down and mounted on bike bases. Plus a silly large pile of parts. All on proper
GW bases.
The downside is I'm in the Netherlands, so postage is harsh. You're either shipping a 2kg or 5kg box (including packing). 5kg is like 35 euro, but maybe less. All insured and tracked and whatnot.
I've also got 4
GW cases, 2 old style, 2 new, various bits of foam missing.
Let me know if your keen, I can take some pictures or skype so you can get a good look at them.
I'm not going to finish painting the army ever really. I _might_ get all the projects I'm keeping completed. But I doubt it. A wall needs plastering, floor relaying, rooms tidied and cleaned. Newel posts needs drilling and installing. Springs here so I should top the trees before one borks a neighbors shed (Chainsaw! CHAINSAW! CHAINSAW!!!!11!!!). I also have a 4 month old to watch, feed, entertain etc for about 12-14 hours a day. But he sleeps, so I get stuff done then.
Maybe paint a squad, or model a BB team. Or mega up a Nob

But I'll not be playing
40k for years, if not decades.
I can more for it piecemeal, but postage is a paaaaaaain in the butt these days, eBay often ends up costing me as much in fees as I make. So job lot works better for me, and you can get some army cases.
Please
PM me with questions, and I can get you more details.
*******
Enough of me shilling

in general response horde is a very fun army to play. Have to learn to play a bit faster, and er on giving your opponent the best of the odds to speed things along. You can lose an awful lot of models and still win, and the other player can roll a lot of wounds and feel awesome too.
Getting second hand models is indeed your best bet. Mostly you need an intact base, and a way of building the model from there. The further along this process the better. A couple of hours adding arms and heads, and a spot of filling can do wonders to someones bitzbox boys. I used to purchase boxes of
GW bits that was usually a jumble of hobby interests. Clean up the valuable parts, flog them, you get your money back and models, plus bits. If you need more 25mm legit round bases then the
LoTR game uses them, and they show up frequently in exit boxes. Plenty of others do this, and it's a gamble. Vague descriptions are good. Imagine piling your stuff in a box, and having your mum describe it.
You could sort of do this with
AoBR when it was at it's launch price. Since someone would want an A5 copy of the rules, a termy squad and dread pretty much right away, that covered most of your cover price. You then had a
tac squad, pair of characters, 25 orks and a trio of deathkoptas. Sad to say, I could sell flying bases far easier than koptas. But they make a nice basis for a dread/Meganob, or any childs toy you'd like to orkyfy
I *love* making my own minis. Orks are great for it. Why does it not look standard? Because it's not!

Big gun on shoulder + supply pack = loota, ranged weapon = shoota, bow = . Grots with spears and shields, just pop a looted gun on a sling.
Anyway, thanks for reading the essay. Best of luck with the greenskins. Remember, quantity has a quality all of it's own. Bring more dice