Unless Patrol Base are local to you and you plan to buy in person, there are lots of good dealers.
My go-to dealers for distance buying are Land Warrior or Airsoft Zone and there are lots more.
I think you have to weigh up what you are looking for.
Unless you enjoy tinkering with electric guns and plan to upgrade, I would look at solid reliable stock guns, You shouldnt have to tinker with springs straight out.
For an M4 variant, I would at least look at the G&G range, They have a budget range which uses a lot of plastic in the build but are great starter guns or an advanced range which are a bit nearer to real steel heft. They also have blowback, but imho this is just a clunk and nothing like real action. All AEG sound like sewing machines to me lol
When you are budgetting, remember that as soon as you get your rifle, you will no doubt start wanting to accessorize.
Optics, spare mags, maybe a sling, Its very easy to overspend.