Hi Megan,
I have a Garrett AT Pro and a Quest Q40. I feel the Quest Q40 is about as capable as my AT Pro, pin points super well, I mean super super well, and the programed modes are excellent. You've got modes 1 and 2 you can set up your self as you gain a little experience with the detector. It costs about $470 from Kellyco and comes with most of the accessories you need, like a digging tool, pouches soft detector bag, and such.
You will want a pin pointer sooner or later as they are a great help when digging a target. I have Garrett Pin Pointer "the famous carrot" and it works very well, but I also have an GP Pointer that works great. It's a clone of the Garrett Orange Carrot with out the various modes and has a little less depth penetration. You can get a GP pointer for about $45 on Amazon and it should serve you well vs $127 for the Garrett. With the $470 Q40 package from Kellyco and most likely a number of online shops and the GP Pointer you will have everything you need to get started for around $515 give or take a little.
You may want to eventually get a purpose made shovel for digging plugs that will make it easy to dig and will help you leave the ground much as it was before you dug your hole. Depending on the make the shove it will set you back from $50 to $100 dollars.
The Q40 is water resistant not waterproof like the AT pro is but ours works better in wet sand and in the shallow surf. I don't get to the beach very often (six hour drive) so I don't have much beach experience. But I do know I put it in beach mode, ground balanced it and it worked really well. My AT pro was great in the dry sand and seems to detect a tad deeper than the Q40 but did not like the wet sand of surf all that much but it will work.
The Garret AT Pro sells for about $550 at Kellyco and comes with the same accessories as the Q40. It has several very nice features that you will come to appreciate like Iron Audio and its extremely user friendly and of course you can count on Garrett to stand by their products. If you don't intend to use the detector in salt water conditions it might be very well be the better detector for you for a small amount over your $500 price point.
Hope this helps a little. Bruce