1)go and get second hand xr6 turbo exhaust cat back for 100-150 and another 100 to get it fitted,,,,
2)then go and get your cat converter changed with a magna flow 3" metalcore one,,,they are normally 450fitted at the exhaust shops but go and get one from ebay (get magnaflow brand) around 200 and pay another 80 to get it fitted
3)then get a performance headers. if you have money go and get pacemaker 4490 or 4495 depends on what you wanna do. 4490 for a streeet use and it gives you power at the lower rpm and if you wanna gain power at the high rpm go and get 4495...4495 is for a track mostly...or there is another option and you can go and get a redback brand extractor which is cheaper than pacemaker.
4)then get your air induction changed, dnt have to spend big $$$, just go to ford and but ford fpv typhoon air box kit. you will receive different airbox with a second intake tube on it amd wotha bigger snorkel. this kit will give you decent performance and it is only $170 dolars and very easy fitting, only takes 20 minutes, also you hve to change your air filter to k&N air filter. k&N panel filter is about 70-80 dolars.
5) now you have to get a flash tuner to get your car tuned and this is on special at the moment...you can get it from KPM in NSW or you can get this from Bluepower racing development in Victoria. these two places are selling on a special price of $450-$460 at the moment. they are normally around $600-$700. you will just plug this on your car and it has soem tunes in it and you will press the button and it will upgrade your car's ecu and your car will run better and it will make you gain extra rear wheel kw.
if you do what i have told you up to this point, you will gain 27-30 rear wheel kw easy....also you can get underdrives fitted on your car to make your car rev quicker, amd this is around 400-500, depends on where you go...
if you want more power there are some other options as well to keep getting done...

6) now you have to get a transmission cooler, because factory one is crap and it makes the coolent get in to your transmission and in a time your transmission will be gone and you will get a bill of 2500 at least,,,,transmission cooler is around 200-250 fitted. there are threee brands you can trust; b&M, PWR, and motorcraft....and also you have to get your transmission fluid changed to transmaxZ...this make your transmission last much much longer and only this oil wnt demage your transmission....
7) now the biggest change on your car will be diff gears and lsd,,,,if you wana good take off, you have to get your diff gears changed to 4.11 and also get your diff changed to lsd one....this will cost you anywhere around 1400-2400. depends where you go and which parts you use....
8) hi stall converter,,,,this will make you rev much faster and you will pass the lower rpm quiker,,,,ba is very slow car on tha take off because of its weight, but with a hi stall you will get shock....this isnt must but diff gears are must on ba series cars,,,
9) then you can get cams, stage two crow cams. they are normally 850 but there is a guy who sells them for 650 on the fordforums.com.au, and his nick is nosxr...everyone gets from them....if you math your cams with a hi stall, your call will be amazing, you will get 0-100 around 5.2 sec,,,if you get all the works i have listed....
10) now at this point you have to get a custom flash tune. you have to take your to the decent tuner and you have to get your car custom tuned, which is around 500-750 depends on where you go and experience of the tuner....if you are in victoria, i will say bluepower racing which is the best shop in australia/////