I have some different suggestions, but I think it is worth your reference.
AEA CHALLENGER I think it's the best bullpup choice under $500.
But because they are new brands, many people haven't heard of it.So if you just count the votes,You may miss it.
Here I'll say the reason.
1.For people who are just starting to play PCP.Calculation costs are often wrong,Because the PCP is more accurate and powerful, you will shooting much longer than other kinds of airgun.so the pellet costs more, you need better riflescope.You need to think about how to filling it.So the consumption plan you learn from other air guns is often not enough, because you play pcp for the first time, so it will be underestimated.I think all friends who have PCP will agree.So you ask under $700, but I think $500 would be better for you.
2.AEA challenger is very powerful. .22CAL 70FPE .25CAL 80FPE ..30CAL 105FPE. You'll find that it's much higher than other similar products.pay attention! it has. 30cal and the price is the same.You may not choose 30CAL at the begining.But it has a 30cal model, means that you can easily buy replacement parts if you want. then you can easily have two cal.Other bullpup gun have no choice at this price.You can think about how expensive a 30 CAL gun is.
3.Some people think that it is shallow to look at power.But without power, you can only shooting light pellet. play PCP for the first time do not necessarily know that PCP should be matched with the correct velocity.If your pelltes are not heavy enough, it's hard to shoot long-range outside.No matter how accurate the gun is.Wind will make you crazy.But if you don't shoot long range.Why should you pursue high precision?So power is very improtant.
4.Some people may say that huge power is too waste air. you can just shot few times per filling.That is right.AEA CHALLENGER The volume of the cylinder is 330cc.This is also a big cylinder on the market.So you can got enough good shots with big power per filling.
5.This gun has power adjustment system,you can use any light pellet And don't worry about speed too high(PCP more than 1120FPS The accuracy will be ugly). You can use heavy pellet for long- range shooting.Choice is better than no choice, isn't it?
6.Many friends recommend P15.Challenger's stock is better than P15. Although the wood is same cheap, But don't forget they're all budget guns.So challenger has better workmanship than P15.
7.The most important thing is accuracy.AEA is a new brand, but now we can see the information and video,Their accuracy is very good. Even their budget gun series.So you don't need to upgrade the barrel.Their barrel is very special, and both have good accuracy when use pellet and slug.You may not know that some barrel with choke is not accuracy when shooting slug .It's important for long-range shots.For example, when FX introduced slug, it also introduced a new barrel.So you will find this phenomenon no matter with the price.
That's why I recommend challenger.Even if the price goes up to $700.I'll still recommend it. It also has these advantages in $700 range.In the $500 range bullpup gun, of all the options I know, it's basically invincible.It's just my opinion.