Can't be done with $1000...at least 5000-10000....If he can buy 2-3 PR9 links for 6 months...i.e about 500/month per site....Then it is possible
PR7 in 6 months ? Ouhaouuu. It's a great deal ! Tell us if you've reached your target. For what site ? When do you start the timer ?
I came across a thread selling PR 7 permanent link for $350 today at DP. Maybe you can try that out. You should get PR 5 for sure, and can get PR 6 if you are lucky, and the page has less outbound links.
I recommend you to be careful while purchasing text links. If possible, but only from related sites, without much outgoing links and not linking to spammy web sites(mostly casinos, realestate etc.) Buying a large number of good PR 6 / PR7 site would be a good idea, rather than buying from a few PR7-PR9 sites. Links from high PR sites are more likely to be reviewed and penalised by google algo. There has been pretty good reports that even links from PR8 sites not helping much with PR and in some cases no SERP change, even if PR increased. http://www.text-link-ads.com/link_calculator.php may help you to roughly calculate the link price. Will not be a bad idea to contact some well known forums / niche directories and other sites in your target area and directly deal for a link. Link exchange sites take a large cut and also place unrelated links which you may want to avoid.
Now that google is coming hard on sites selling links that is not passing the link juice, in 6 months it would almost impossible to move to PR 7.
So its means the only way to get pr7 is buy paid links of pr 6, 7, 8, 9. $350 pr7 link.... not bad ... according to it if someone buy 10 pr7 links he should spend $3500 too costly. any chepaest way to get pr7 with budget $1500??