Paid Competiton Script

I am in need of a script for a competion site with a difference. To enter the competitions, you need to pay a certain amount of points, e.g. 100 points = 1GBP. The first stage needed is the user payment side. The user needs to be able to purchase any ammount of points using a paypal IPN. I.e. if they pay 5GBP then their account is credited with 500 points. That section shouldn't be to hard. The next stage is to build the comptetion section. I (the admin) need to be able to set-up various competitions of different price. I.e. some may be 100point entry while some might be 10'000 points entry. This is where the site becomes different from others. Each competion has only a maximum of 100 entries giving every applicant a much better chance of winning than other competitions. I would like this to be customisable, i.e. offer 50max applicants or even 10max. Each user needs to be able to enter as many times as they want to with the points they have availble. I.e. If they have 500points and it is a 100 point entry then they can enter between 1 and 5 times. Once the competion has had it's maximum applicants then the entry section must be removed and a winner be automatically chosen at random by the site. I (the admin) and the user needs to be notified of winnings. That is all that needs to be done. In the email i should be able to customise what is said so i can give them direct instuctions in what to do. Any questions, and i'm sure there will be, please direct them through the PMB. I will try to answer as quickly as possible. Many thanks!