If you are worried about budget and you can’t just 3D print an army, I’d say orks are a lot more forgiving. There is a lot of 3rd party ork stuff, and since their aesthetic is ramshackle, it is quite easy to build ork tanks, walkers, vehicles, and artillery essentially from scratch.

Now, all of that assumes you don’t care to participate in official GW tournaments, which are unfortunately quite strict on the policy of only using official GW figures. I think that is a far too constrictive and greedy policy, especially given how much in the past GW encouraged scratchbuilding and conversions. If you are playing with friends or an an independently run store, using 3rd party or scratch figures usually isn’t a problem, especially if you make good looking ones where it is easy to tell what they are supposed to be. I think converting and scratchbuilding is a major part of the hobby and encourage it personally.

As for what the models are armed with, What You See Is What You Get is the accepted baseline. Models should be using what they are modeled with. This is the official tournament rule. Again, in casual play or even independent tournaments it is normally fine to “proxy” in models as if they had different weapons so long as the opponent agrees to it. This aspect all revolves around courtesy- if you are making reasonably proxies and especially if you are marking them in some way (a sticky note or something even following the squad around), then it is reasonable for an opponent to agree. If you try to proxy every model in your army as using some different wargear than what it has, it becomes frustrating for an opponent to keep track. Just, try and keep things within reason and you’ll find that most people are reasonable in return.

If you want a good start and you haven’t painted before, going on ebay for a used infantry box wouldn’t be the worst idea. Get some used condition models for cheap, strip them if needed, and paint them. An army always has a use for at least a squad of infantry, and you can make your painting mistakes on those before committing to more miniatures.

In fact, if you have an independent store with a good community you should check if it has any open night or Kill Team nights. Kill Team is a good entry point for something in the process of putting together their first few models, and you will likely meet somebody willing to play a starter game with you. From there, you can keep building minis and transition to the full game if it seems like a good fit.

A final factor when it comes to the hobby is the cost of hobby supplies. Don’t go crazy right off the bat and buy a million shades of paint because a tutorial told you to. Slow down, get a few foundational colors and a few main colors you’ll be using and learn. I reccomend looking at what is offered by a variety of companies not just GW. AK, Vallejo, Army Painter (not my choice), Tamiya, and other brands all have products and it is acceptable to pick and chose. I make my own washes out of artists ink, which is more long term cost effective, if you decide to stick with the hobby. Even the bottom of the barrel Applebarrel or Folk Art craft paints have a role, especially if you are trying to reduce cost. Get some good brush conditioner to help keep your brushes in good shape.