Tacticdesigns, I was not recommending she buy the expensive, but renting is certainly an option. Also, don't mean to burst your bubble but it seems you're giving advice on something you don't seem to know so well yourself. The shots you posted of the stock cars are god-awful and I would only ever post the as an example of how not to shoot sports. Also, I'm pretty sure an AFL field is wider than 150mm
OP - I'm confused now as to what sport you are talking about - did you AFL as in Aussie rules footy (what I had initially assumed)? Or American Football? Aussie rules with its large oval fields gives greater working distances than a square field. I think the best advice is to do as gryphonslair said and forget about peak action shots, slow the shutter speed down a bit and focus on smaller details.
I am going with the Australian Football League since the AFL no longer exists here in the US and it is the off season for the NFL of which the AFC (former AfL) is a part. There are no American Football League games at this point and training camp is many months away, thank God. I am still busy with basketball, volleyball and indoor track and am preparing for spring baseball and track and field. I don't need any Football right now.