Is it permissible to try to deter the rivals from bidding a contract by offering money?

The job presented for a contract receives its real price by the offers of the bidders; the loss of the owner of the job can be prevented only that way.
It is not permissible for a bidder to get the contract by giving money to other bidders secretly and persuading them to withdraw from the contract. That kind of behavior cannot be regarded as an honest agreement. And it is not possible to say that the money accepted in order to withdraw from the contract is halal (religiously allowed). To abandon bidding is not a work requiring payment.

It is better to call that kind of things as corruption in contracts and tricks to bankrupt rivals. As it is not right to try to deter the rivals from bidding in contracts, it is also not right to offer more prices than one can not afford to provoke the bidders and compel them to buy things in exorbitant prices. To offer a price that one cannot afford and to cause an increase in the value of the contract is najash (trick) in the Prophets words. And it is not suitable for a Muslim; it means just provoking the rivals to harm others.